solo travel recommendations

hi all! i am planning on taking 2 weeks to travel around central europe at the beginning of may. i am coming from the US and have solo travelled around the UK/Italy before. some cities i have in mind so far (not set in stone) are amsterdam, berlin, vienna, somewhere in switzerland (would LOVE recs!), lyon and/or paris.

are there any particular cities you would recommend that feel safe/you loved?? i am also not opposed to going off the beaten trail and staying in less touristy areas. i love nature and hiking so very interested in more nature forward areas!