I know you can visit some theme parks at certain times of year to avoid many children, however what I mean are theme parks built more for imaginative and fun-loving adults.
Take some of the park rides you might find in family theme parks that appeal to both adults and children, but instead of avoiding elements that may confuse/frighten children, they're allowed to get more detailed or whatever may be more fun for people. Fwiw I'm aware of some smaller scale themed venues (particularly some horror-related ones), but I feel like I'm blanking on any obvious larger scale ones.
If a bunch of them have coordinated a themed red light district, I guess that may count for the most explicit approach to this idea, but I don't know of any that have, albeit maybe parts of Vegas have given that a run for its money.
Universal does Halloween horror nights that is very adult oriented. It's in their normal park but they are open a standalone Halloween themed park in las Vegas soon that will be similar but full time.
Worlds of Fun here in KC does this too. Kids can enter, but the do not recommend they stay after dark. They have a parade, have entire areas that are outdoor haunted houses, and send people running through the crowd to scare them. It is a lot of fun. Most of these regional parks are all owned by the same company (Six Flags, IIRC).
Busch Gardens if you want a theme park that’s also a zoo and botanical garden and has a lot of alcohol because its purpose is to advertise Anhauser Busch beers.
EDIT: Kids are allowed, but the alcoholic attractions are designed for adults.
There's an amusement park in Maine that does "after dark" a few nights per year. Adults only and they serve drinks. It's marketed toward millennials who grew up going to the park. I haven't been, but it seems popular.
Fuji Q Highland in Japan has a lot of record breaking attractions and coasters and is more popular among adults. There are some areas catered towards children but these are fairly well sectioned off.
I don't think I've ever heard of one, and I'm not sure if it'd be profitable. I mean, a lot of elements of theme parks are designed to extract money from parents, and only work because they are there with a child.
How would the adult theme park make money? Expensive entry tickets maybe? We would want to avoid alcohol because we don't want people acting without inhibitions near all this heavy machinery, plus it'd make cleaning more expensive, and might cause more vandalism. I guess you could not allow re-entry once they leave, to force them to eat inside the park. But that's about all I can see happening. You could put a nice sit down dining place inside the park though too, because the audience would be more into that sort of thing.
How about the decor, what kinds of thing even appeal to adults? This one is tough. Maybe a western, or dystopian future theme? That could be cool.
You'd 100% be selling overpriced alcohol in an adult-centric theme park. If Six Flags and even Disney have figure out how to do it safely (and very profitably, I'm sure), so can other theme parks.
Honestly any, even if I may never get a chance to visit, I like learning about some of them, particularly ride designs and engineering. (Also for those lurking, this question is mainly inspired by having watched some more Defunctland videos lately.)
Honestly, I wanna know as well. I've been enjoying Carowinds and I enjoyed Universal, but they're both quite family-oriented. Maybe Cedar Point is more adult? Seems like they have lots of big rides... But they also have a Camp Snoopy area there...
I'm so glad I'm not the only person that gets the same "theme park" vibes from MMOs. It really takes me out of it when someone is doing the same quest as me but is a few steps ahead so they trigger a unique animation or dialogue from the quest giver, and then I experience the same animation or dialogue a few minutes later. Kinda like waiting in line for a ride but you can hear or see some parts of the ride as you progress through the line.
You might enjoy cruise ships. They get a lot of hate but they're an amazing vacation.
Endless adult-friendly activities at the destinations. All you can eat gourmet included in the price of the ticket. World class service from staff that actually cares. You even get to know the housekeeper on a name-to-name basis. Not to mention waking up to a different view out your balcony every morning. It's worth it for that alone.
Boring as fuck if all you do is get wasted. You have to sign up for the excursions. Why get wasted when I can hop on a water jetpack or swim with wild dolphins?
Theme parks are very expensive to build and run, so it's not usually financially viable to limit the audience like that, but they usually have some rides that are fun for adults. Or they have to be smaller scale, since it's a more niche audience.