Yesss, Aqueduct! After playing a bunch of Empires, Aqueduct has become my favorite landmark, next to Defiled Shrine.
If you only read the card rules, you might think that Mountain Pass is the only landmark that sets up an auction. Not true. Aqueduct sets up an auction too. Anyone wanna gain an estate for 2 VP? No? Let's raise it to 3 VP. Then 4 VP, and so on.
This is basically a "dutch auction", where it starts with a high asking price, and the price is gradually lowered until someone bites. And then once it's over, another auction starts. But each auction has a different value, because gaining green early in the game is awful, and gaining green later on is less awful. To play well with aqueduct, you have to have a good idea of how much green hurts you and your opponent at various points in the game.
Of course, you can also do a few cute things with gaining treasure and green on the same turn. One time I went for Treasure Maps and bought an estate on the turn they collided.