What activities would you not recommend to do as a solo traveller?

Hi everyone!

Recently I did a solo travel to Italy and while I was in Milan, I went to the OC Terme Milano Spa because all of the trends in TikTok about the Rain Room.

What I didn't expect was that everyone there was with a partner or in a group of friends, there was no other solo traveller around.

So it made me wonder, what other activities would you not recommend because it can seem too weird or awkward to do as a solo traveller? Not like the necessary things you might have to do like dining alone or going in a tour, but actual activities that sounds fun but are not though to do it alone, like fancy vineyard/wine tours or workshops.