<human>: I thought I would never make one of these itinerary posts but here we are, I'm stuck. 

My boyfriend and I have 3 weeks and a bit of cash to travel around Europe in October. 

We'll probably spend the first five days in Berlin seeing friends, because flights from London (where we live) are dirt cheap. Boyfriend lived there for a while in 2014 but it's my first time so I'd be open to spending longer, if a strong case is made for doing so.  

The rough plan is two other European cities after Berlin. Amsterdam is in the running, but we've both been there. We'd prefer somewhere cheap and unfamiliar (i.e. somewhere not-west). The thing is, everyone has good things to say about everywhere on the bloody continent. People have recommended Croatia, Poland, Prague, Budapest and Bucharest to us—and that is just personal recommendations, the Internet is full of them. We've also thought about maybe Athens + a Greek island (maybe Crete?). 

If it matters: we're 21, and although we are very much on a 21ish budget (anticipate hostels, although small airbnb would be better), we are not really in the market for a 21ish holiday. I love to drink and boyfriend loves music (techno etc) but he's been sober for a year and we're looking for something more Dignified. We like wandering around on foot, sitting at (cheap) cafes, shopping, and an occasional dose of arts and culture. It would be great if the streets of this hypothetical place stayed lively after dark.

NB: definitely want at least one of these places to be REALLY, REALLY beautiful. Cobbled streets and balconies and so on. We wouldn't mind staying in a sleepier town if it's cheap, has some cafes, and is really beautiful. Because we are shallow.

Key factors: 
- Pleasant in October (enough to spend most of the day outdoors)
- Not unavoidably touristy
- Cheap access from Berlin and/or London
- Cheap to have a nice time in
- Beauty!!!

We're very indecisive and all the options are killing us. Pls advise.

Can you give me a shortened version of the text?
<bot>: we'll probably spend a week in whatever European country you recommend most strongly, as long as it's cheap and beautiful.