The German railway, www.bahn.de is the best place to check timetables. You can also make reservations for the German trains here, including Berlin to Amsterdam (if you want. Not necessary).

All these journeys are easy, on good trains. Just search for Berlin Hauptbahnhof (the main station) for Mitte. 

You will probably want to use Thalys for Amsterdam to Paris. This comes with a reservation fee of €30, although you can avoid it by taking much slower Intercity trains. Get a direct Thalys, because if you have to change at Brussels, you'll pay another €30!

Paris to London also has a €30 fee. You can book both on the Interrail website or the Belgian Railways site. These two trains can sell out of passholder reservations, so book early.

Al your trips have direct connections, good frequency, comfortable, fast trains with plenty of amenities, no change needed.

When do you plan to book exactly?

It might be worthwile to check ordinary saver tickets and compare then with prices of a pass + reservation cost, since two of your trains have hefty reservation costs. Trip 1-2 are best bought on www.bahn.com Trip 3-4 can be done on NMBS/SNCB International.

If you decide to go for a pass, book your Eurostar (Paris London) ánd Thalys (Amsterdam-Paris) as soon as possible, as they have pass holder quota, so they can sell out.

Thanks for the above replies! I just reserved seats on Amsterdam → Paris, and Paris → London. Phew!

For my other two trips (Frankfurt → Berlin, Berlin → Amsterdam), I am seeing “NO SEAT RESERVATION REQUIRED” and “You can buy a seat reservation if you like but it's not required.”

Does it make sense to still reserve seats on these trains just to be safe, or is it not necessary?

Is it better safe than sorry for a reservation, or am I just wasting money securing seats?

It depends on date and departure time. You can check bahn.com how busy DB expect it to be. Or just book a seat. It's free of charge via tickets.oebb.at in 1st class or €3 in 2nd. Use Interrail/Eurail as a discount and look for normal tickets, NOT "Seat reservation only”.

In my experience the few euro it costs for German trains are well worth it for even quiet trains. If nothing else it prevents you playing musical chairs if you are in a seat that is only reserved for part of the journey.

Your total spend is hundreds of euros so a few extra for the comfort is well worth it. I have experienced the chaos of full trains in both the UK and Germany from the “luxury” of a reserved seat.

Thank you for the replies! Good call on being safe, I think I’ll book reservations even though it is not necessary. Better safe than sorry.

I just booked Frankfurt Airport → Berlin HBF now, but was looking yesterday and there seemed to be quite a few direct trains from Berlin HBF → Amsterdam Central.

But looking now, I’m not seeing ANY direct trains from Berlin HBF → Amsterdam Central on May 25, 2023 … even though I noted IC146 or IC144 in my notes yesterday. It seemed to have disappeared, unless I was looking at a completely different date by mistake  

Could it be that there are NO direct trains between these two locations on May 25, 2023?

The Amsterdam trains on that week are currently showing as departing from Berlin Gesundbrunnen not Berlin HBF. Possibly some works meaning they are unable to use Hbf.

Gesundbrunnen is just another city station within Berlin and is easily accessible from elsewhere in the city so just think of it as a different starting point.  I walked from Hbf to Gesundbrunnen (because I liked exploring the area) a few months back.  There are a number of U- & S-bahn lines linking it to other areas of Berlin.

If you are interested in WWII remnants you can check out one of the remaining massive Flak towers - https://en.wikipedia.org/wiki/Flak_tower#Flakturm_III_%E2%80%93_Humboldthain,_Berlin - which is just across the road from the station.

I was just trying to book two seat reservations from Berlin → Amsterdam on the morning of May 25.

I’m able to add the seat reservations to my Eurail cart, but later in the checkout process I get the message “One of the legs of your journey is not available anymore. Please try searching for another connection.”

The train is IC 146 … direct from Berlin Gesundbrunnen to Amsterdam.

Am I doing something wrong? I am hoping for a direct train so the journey is as relaxing as possible.

Help? :)

Don't book a reservation for this train via Interrail. Way too expensive (€8) and doesn’t always work.

Reservations are €3 on tickets.oebb.at.