Phoeh, there are quite a few.

I’lld say, dare to stray from the trodden path. Europe is much more than it’s biggest cities/capitals. If you’re daydreaming and staring out of the window, and you see a nice looking city centre, castle, church, station building,… Get off and explore it a bit! You’ll probably won’t get disappointed.

• I really liked Aarhus (DK), calm small town vibe, but quite a lot to do. It was the European capital of culture a couple of years back and has funny traffic lights with vikings. It went trough a remarkable urban renewal and has very nice museums, like AroS and the Moesgaard museum (very impressive building as well). Lovely places to eat and drink! Very nice, cool and laidback vibe. The surrounding environment is rather nice, with some woodlands and pleasant beaches.
• Another tip is Pitlochry (Scotland). Nothing more than a small Victorian town north of Perth, but it’s situated on the foot of the highlands, alongside the Highland Main Line from Perth to Inverness. Despite it’s small size, it had a lot to offer: nice restaurants, a lot of hiking paths, a lake with watersport possibilities and the Pitlochry festival theatre, just next to the woods and rivers with a lot of famous plays (mainly in summer). An ideal combo between nature and culture this location. Please note the cute little station, that has a little 2nd hand book shop in it. The Highland Main Line is also rather scenic, and it’s not too far to enjoy a heritage train at Aviemore.

I found the city center of Lille (France) nice on my 2 hours layover between two trains last April. It was a nice surprise to see a very interesting city center. (by plane I would never had this sort of experience)

Maybe someone can confirm (or not). :)

Had it not on my list before, but after that I will consider to get there and visit the area.

​@BrendanDB Last year I went on a trip from Venlo (Netherlands) to (Bergen, Norway) I took the ferry from Hirsthals (Denmark) to Bergen). I had about a two our stop in Aarhus. I didn’t go into the city center. REGRETS! I definitely want to do a similar trip and next time I’ll be sure to actually spend time there.

Also great tip on Scotland! ​@ralderton suggested a really lovely sounding route on this post. I think I’ll patch your suggestions together for my Interrail trip to Scotland. That is hopefully my next Interrail trip :) 

​@Angelo I can confirm! I also had a layover in Lille and did go in the city center. It was definitely worth the visit :)