I don't know if it specifically notes it anywhere, but most of the Unique Features give a "We love our National Parks!" +1 happiness bonus, excepting Epic Lairs (Pyre of the Seraphic, Brandelines Well, Aifon Isle, and Broken Sepulchur), the Guardian of Pristin Pass, and Remanants of Patria ( which gives +3). They must be in the BFC of a city to work, but can affect multiple cities if their BFC's overlap.
More specifically, Mirror of Heaven provides 1 sun mana, and +6 sight range.
Pool of Tears increases healing by units on the tile by 30%, and removes disease, poison, and withered. Possibly more.
Ancient Towers just give +5-6 sight range, and can be destroyed by building improvements over them. That's nice, since they basically suck after the early game, and would be much more useful as a farm or cottage or workshop.