So, aside from brothels and such, I gave this question some thought. Here are those thoughts, in no particular order.
Arlington National Cemetery and the Vietnam Veterans Memorial are the most sobering.
The Grand Canyon National Park and Glacier National Park are the most epic.
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The Tropicana and Flamingo Casinos are the most gangster.
The Acropolis in Athens and The Pyramids at Giza are the most historic.
Saint Peters Basilica is the most inspiring. (I bet the Hagia Sophia gives it a run but I have never been there)
Waterloo is the best battlefield. (I have never been to Normandy)
The Horse You Came In On Saloon is the best place to get drunk with Edgar Allan Poe's ghost.
Anywhere in Thailand is the best place to get AIDS.
National Parks are my wheelhouse.
Grand Canyon was cool but I found it kinda sorta ever so mildly disappointing? Maybe I've just seen it too many times in pics/vids. Definitely amazing but I guess I expected a tiny bit more somehow?
Glacier is badass. Going to the Sun Highway is an adventure everyone needs to experience at some point.
Yellowstone stands alone, nothing like it. Grand Tetons (or Tittytons, as my little brother and I called it as kids) are the shit.
Not a NP but coming northeast bound out of Yellowstone there's a road called Beartooth Highway that is some spectacular mountain scenery and scary af switchbacks.
Olympic, Rainier are obviously legendary but I don't need to tell this bored about them. North Cascades is massively underrated though.
Rocky Mountain is very worth it. Great Smoky Mountains is really cool but you have to set aside your west coast mountain elitism to be able to appreciate it.
Arches is one of my favorites, really unique landscapes. It's the only one of the Utah parks I've been to yet though, I definitely need to see the rest.
Badlands is eery. Wind Cave is fun if you have time for a tour.
I've barely been to the edges of Theodore Roosevelt, Petrified Forest, Mesa Verde and Everglades. Really want to do the full Everglades sometime.
Gateway Arch is a NP now which is ridiculous but it's still cool to visit.
Never been to any of the California or Alaska NPs which is a blackeye for me, IMO.