This summer my best friend is coming to visit and so we've decided to take a month to travel around Europe maybe by train.
We're going to leave from Lugano tran station and the idea is to go to:
Côte d'Azur, Barcelona, Madrid, Paris, Amsterdam, Prague, Vienna, Venice, Florence, Rome and back to Lugano.
Any suggestions? Hotels/things to do?

Thank you!

Your itinerary is too ambitious. Two weeks each at the following museums sound like they would be right up your alley:

Cement Museum

German Occupational Health and Safety Exhibition

I second the cement museum, awesome place!

To visit all those places in a month you would need another month of to recover.

Try to avoid places full of tourists, that would mean crossing off a few of those cities, and go a bit slower about it, spend more time in max 2 countries, look for authentic experiences, not crossing off tick boxes ;-)

Yeah it sounds like too much, why not just head out east - you can go out through munich, prague, krakow,, then back through budapest, vienna, croatia, slovenia ... would give you more like 3-4 days in each. Otherwise you only get a day or two in each, so with travelling time you hardly get to see anything. also everything is so cheap out around poland, so you can do a bit more, and you get a mix of scenery, beach and mountains.