I've traveled solo for work and usually stay a few extra days if it's an interesting place. I've enjoyed booking various tours as well as exploring on my own. From Albuquerque, I spent the weekend in Sante Fe on my own visiting art galleries, shops, etc. I usually start chatting with store owners in small shops.
In SF, I took the ferry over to Sausalito and chatted with the wine store owner. I also booked a wine tour. When I told the coordinator that I was solo, she suggested that I take the "lower level" tour in stead of the premium one, as mostly couples did the latter. I met 3 ladies from Scotland and had an excellent time. My colleague usually finds restaurants that have a galley where he can sit at the bar and watch the chef cook or chat with others.
I have also done WDW solo. Once was after clearing out my Mom's house in FL and I just needed to go and chill for a few days: I went to the spa, read a book at the pool at AKV, chatted with others at the pool, ate long breakfast/coffees chatting with others, and sometimes head over to Disney Springs. I pick a TS with lively pool areas and if they have quick service restaurants, it's easy to chat with others. My fav is AKV Kidani for breakfast in Sana as it's quick service and lovely. Sometimes I get coffee in AM at SSR and then sit by the pool. Same for OKW. A DVC resort is probably my Fav solo. I also had an annual pass at the time and just power walked around AKV or the world at Epcot to get 5-7 miles in each day.
Once, I had an entire weekend planned for N. Italy, including a day tour to Lake District and Switzerland, but trip got nixed last minute. I use viator.com to see what an area has. They are a booking agent for local tours. There are food tours, etc. Once, we had a solo Mom (with a baby) on our day tour from Florence! We all had an awesome time!
If cruising starts back, NCL Epic has cool studio rooms with an attached lounge, the have a concierge who coordinates group singles dinners, matches up groups to do excursions, etc. I wanted to use their free espresso machine so badly!
I'd totally do a TUG girls' meet-up somewhere in the future. It would be super fun to "meet" and hang out with my TUG girlfriends. Orlando is likely the easiest as plentiful supply. Maybe fall 2021? We could do a different "Event" each evening with DIY/WDW/meet at the pool during the day: drinks/appetizers ice breaker at Resort X poolside on Monday, Progressive dinner in 3 condos at same resort (I'll be at a Marriott with an AC) on Tuesday, Games night at someone's condo on Wednesday, etc. Elaine(ps. Can anyone tell that I was our HOA's social chairperson for 5 years-lol!)