I think I've seen one:

Parthenon Sculptures (Elgin Marbles) (c. 444BC), British Museum, London

And I'm not certain, I just know I went to that museum. I usually do better on these "top __" lists than this.

You didn't see Stonehenge or the Sistene Chapel during your Grand Tour?

Stonehenge is inconvenient to get to if you don't have a car. You have to take a train and then a bus, and even then you have to stand a good distance away. If you could have walked inside I would have gone, but looking at it from a hill across the way didn't seem worth the trip. I went to Oxford and Windsor and Dover and some castles instead.

I did see the Sistene Chapel, forgot about that. I had it confused with something else. Which is rather stupid. Anyway, so, yeah, I saw two.

I know, 'cause I went there without a car. But you're wrong about the distance thing, you get to go inside, up pretty close. You just can't get within touching distance of any of the stones.

what was so great about the rothko chapel, in your opinion? it was certainly eerie in there, cause it was deathly silent and all, but the paintings seemed better as backdrop than anything else. I saw all I needed to see in about 10 seconds. If there was a concert or something going on that would be swell, but by itself, eh, not so much for me. Although it was nice to get out of the sweltering houston heat.

also, assuming i saw all the "correct" things when i went to the appropriate locations, I saw 20. Good thing I went to the Prado.

Rothko Chapel was very peaceful, and it's worth it just to see a structure built especially for a set of paintings, but like you I had no transcendental experience there.