I'm incredibly fascinated by the Rothko Chapel. The more familiar I become with Mark Rothko himself, the more complex his art becomes.
His work—and his Chapel in particular—is so surprisingly and simultaneously subversive, intense, sublime, disturbing, tranquil, and uncomfortable. Pair this with Morton Feldman's Rothko Chapel composition, and the whole thing becomes this mind-inverting whole that is as beautiful as it is perplexing.