I find the best way is to establish where the main thoroughfare is, and also the old part of town. That's usually where there's shops and nice places to wander about window shopping and looking for food options. Bigger cities often have multiple versions of these things so you might need to walk around a few to get a sense of which ones are touristy and which ones are something else.

Once you sort of have your bearings, think about what this place is famous for in the sense of "when have you heard about this place in an everyday context?". Was there a famous guy who did stuff here? Did something big happen during the industrial revolution? What was the war situation like? If there's any big notable things that spring to mind, chances are there's a museum or monument or thing about it. And obviously what springs to mind is going to be different for different people. You might instantly go to some botanist who worked for the national gardens while I might think of some architect who designed a bunch of metro stations, while someone else thinks of that really well preserved tank they have. Don't go "I have to go to these places because they're famous", go "oh that's where that I thing I know is!"

Alternatively, super niche but if you still use Pokemon go/Ingress, open it up and see where portals are scattered. Generally speaking if there's a lot of portals in one area, there's something interesting there. Also idk about Pokemon go but ingress has a 'missions' mode where people make little pseudo-orientering maps where you have to run about looking for a specific location, and they're often themed.