Here is a good route :

- Bruxelles-Midi - Köln Hbf 08:23 - 10:15

- Köln Hbf - Basel SBB 10:55 - 14:47

- Basel SBB - Lugano 15:03 - 17:58

- Lugano - Milano Centrale 18:02 - 19:17

- Milano Centrale - Siracusa 20:10 - 15:48 The train goes onto a ferry across the Messina Strait. Incredible !

In case of delays I'd advise to leave Brussels 2h earlier and enjoy dinner in Milan before the night train.

I don't think a pass will be good value for a trip like this. Use bahn.de from Brussels until Chiasso and then trenitalia.com. There are very cheap tickets when bought well in advance.

For example on 5th July :

- 06:23 Bruxelles-Midi or 06:34 Nord - Chiasso 59.90€ !!!

- Chiasso - Milano Centrale 5-10€

- Milano Centrale - Siracusa 45.90€ shared couchette compartment or 104.90€ for a private sleeper cabin

Incredible value for money in my opinion

Let me know for questions

To find the bahn.de ticket add "via Mannheim". You can tweak the ticket on the website and add a 1-2h break in Basel (seems like a good idea to me). If you want such cheap tickets buy well in advance (or even right now). 

For the return leg I'd also take the night train :

- Siracusa - Milano Centrale 13:35 - 10:10

You could make it to Brussels (or Antwerpen) that night but it is quite risky because the Milano - Mannheim train is often delayed.

- Milano Centrale - Mannheim Hbf 11:20 - 17:58

- Mannheim Hbf - Frankfurt Flughafen 18:04 - 18:35

- Frankfurt Flughafen - Bruxelles-Midi 18:42 - 22:35

Bahn.de doesn't sell a ticket with those connections because it is too tight. Per rvdvorgt's advice going all the way to Brussels would be possible but only on specific Sunday evenings (not all due to engineering works). What would be your travel date ? 

It seems that there are no saver tickets on the direct EC train Milan - Germany so here is a good connection that works :

- Milano Centrale - Brig 11:20 - 13:16

- Brig - Basel SBB 13:48 - 16:01

- Basel SBB - Köln Hbf 17:13 - 21:04

- Köln Hbf - Bruxelles - Midi 21:42 - 23:35

As an example on 23rd July :

- Siracusa - Milano Centrale - Brig about 100€ (not available to book for the moment)

- Brig - Bruxelles-Midi (arrival 23:35) 56.90€

Best on a Sunday evening, where there's a late ICE to Brussels as a fall-back.

Thanks very much @rvdborgt !

It doesn't seem to run every Sunday though, surely due to engineering works. AFAIK (per bahn.de) it would be possible on :

- 23rd and 30th July

To get this connection (arrival 23:35 in Brussels) again tweak bahn.de and add a 1h stop in Mannheim or Cologne.

It is also kind of possible on 16th July :

- Mannheim Hbf - Köln Hbf 18:36 - 20:04

- Köln Hbf - Aachen Hbf 20:15 - 21:07

- Aachen Hbf - Bruxelles-Midi 21:18 - 22:35

Probably. There are engineering works until 14 July around Cologne, delaying ICEs by an hour.

I took a much more relaxed journey from Siracusa to Brussels (then London) last year.
Siracusa on morning IC to Salerno (approx 1000 to 1800)

Salerno to Bologna on Frecciarossa (high speed)

Bologna to Nuremberg (via Munich)

Nuremberg to Brussels (via Frankfurt)

With a global pass this would cost about 30 euro in reservations/Brenner supplement.

For the single journey the cheapest advance fares (limited or no refunds or exchanges) would be about 300 to 400 euro.

So the return journey would be 600 euros with no real flexibility versus a 10 day in 2 months global pass at 421 euro for an adult plus reservations. There is also a 7 day pass for 352 euro.

Given the opportunity to hop on or off and flexibility to change unlimited times right up to minute you board a train it is a no-brainer - poor flexibility of advance tickets or flexibility to use peak time trains and change plans and a fixed price (other than reservations).
 

Also if you do go to Siracusa check out Casa Alfeo on booking.com (An apartment with a great location).

As you may have gathered trains across Europe are great but do take time and changes.I would look at needing 2 very long days or 3 reasonably long days from Brussels to Siracusa. I would not travel on night trains (a personal reluctance to either sleep with strangers and a small bunk or pay a fortune for privacy - almost all with a shared railway toilet at the end of the corridor. Give me a cheap B&B or IBIS with en-suite anytime).

Last piece of advice (before your questions !) :

It seems that the direct night train to Milan arrives at 11:27 on Sundays which is too late. Instead I'd take the night train to Rome and then a high-speed train to Milan. More expensive but you leave Siracusa later !

- Siracusa - Roma Termini 19:10 - 07:18

- Roma Termini - Milano Centrale 07:50 - 10:58

- Milano Centrale - Brig 11:20 - 13:16

Should be about 100€ (maybe 150€ for a private compartment)

But keep in mind that the full Italian summer timetable hasn't been published yet...

@Yorkie It's true that this journey could be done on multiple days but @Pindakaas has only one week in Siracusa. The night train is a great way to travel in my opinion, especially when you can have a private cabin for not much more.

And for this journey I don't think either that a pass will be worth it.

We shall agree to differ - I cannot see how using a train from Belgium (or UK) would ever be suitable for a one week holiday in Siracusa. You need at least 2 days solid travelling, even with a night train each way. The fastest would be Brussels - Milan in a day for the evening sleeper? That would need a high speed service early to Paris then the Paris - Milan TGV or Freccia service.connection.

Just about doable for 150 euro to Milan and about 40 mins before night train connection (with station change in Paris)

Then a 20 hour overnight train journey (If you can get a berth). That costs between 50 and 100 euro.

I flew to Siracusa and returned by train and fully enjoyed the 10 days I took.

IMHO night trains do not appeal - If travelling as a single the 20 hour night train from Milan/Rome to Sicily has no catering, almost all cabins are shared or carry a premium for single use and the toilet facility is a joke. Also there are very few sleeper places available for summer and the pass non-cost for a single room is about 100 euro (when available).

Have you actually done a realistic costing before saying you do not think a pass is good value?

You tell me your cheapest route and I will gladly cost it for you with dates/times and train type. I also cost on both the cheapest for the trains I would use and the price of a comparable flexibility to a pass.

You need to consider dynamic pricing so booking months ahead to get cheap rates. (Reservations excepted for key trains such as sleepers and Eurostar).

Remember that a pass lets you use your choice of train, irrespective of peak times and totally cost free changes. except losses of reservations if not refundable.

There are also lots of small savings for local trains on travel days - e.g. s-bahn trains around German cities on an evening. 

Yes I exactly added ticket prices for that reason in my post. See my above posts (with dates in July)

From Brussels you do not go via Paris, it is indeed a waste of money. It is very easy to go via Germany and Switzerland and you can benefit from DB incredible saver prices. Brussels - Tirano (incl. Bernina Railway) can be done for 40€ as an example, obviously you need to book in advance but this is an example. Alone Chur - Tirano one-way costs double than that.

You leave Brussels in the morning, arrive at 6pm for dinner in Milan and then take the night train all the way to Siracusa.

About 160-180€ per way (summer prices, see above) including a private compartment. For only this return journey a pass will cost more. Why ? Very expensive surcharge for the private sleeper compartment.

@Pindakaas has (or will have) set dates so it is no problem for them to buy advance dates.

I'm all for the pass but for a fast return journey it is not worth it. If OP were to stop for 2-3 nights along the way I'd advise the pass.

"For example on 5th July :

- 06:23 Bruxelles-Midi or 06:34 Nord - Chiasso 59.90€ !!!

- Chiasso - Milano Centrale 5-10€

- Milano Centrale - Siracusa 45.90€ shared couchette compartment or 104.90€ for a private sleeper cabin"

So you think that 2 journeys starting at 6am and arriving the following afternoon with 20 hours on a train with no catering (except a few snack items from the train manager) and costing about 400 euro return are really attractive - I would rather do a 13 hour long haul flight to Las Vegas (and that is hell). At least you get fed and watered and probably just as much sleep. OK I accept that the toilets on a flight are also shared.

A 4 day pass would only cost (for an adult) 258 euro and reservations using daytime trains over 2 days each way on your routing but with a daytime FR/IC option would be less than 100 euros allowing enough for a moderate hotel or hostel each night. For youths or over 60’s it would be less.

People have different views and tastes. The OP asked for advice on a train journey from Belgium to Siracusa, so there's every reason to give such an advice, together with some price examples. The OP can decide for themselves whether a pass or advance tickets are the better choice.

I did the other way around in October, by the way, and that went quite well. We had a warm lunch in Cefalù (from there night train to Milan), brought sandwiches and drinks for the evening, had a small breakfast from the sleeper attendant in the morning, had coffee on the train to Zurich, bought some more sandwiches for lunch, then had dinner on the train after Frankfurt. That was after 1 week of Sicily, all by train.

I get reasonable sleep on a sleeper, and although I sleep better in a real bed, I can function normally on the day after a night in a sleeper. If a sleeper don't work well for you, then of course the whole equation changes.