Wat Sensoukarahm, Luang Prabang, Laos.
You haven't done Asia until you've done a temple stay - so sayeth a snobby backpacker I once met.
I hate to admit it, but that snobby backpacker was on to something; nothing replicates the experience of breaking bread with a monk, discussing the world at large on sacred ground, saying your prayers, and sleeping in an ancient temple.
While Luang Prabang is a wildly popular tourist destination, few folks know that it's possible to arrange a temple stay at some of the region's oldest and most venerated wats. All you have to do is ask around - and since local monks are famed for their openness and kindness, you shouldn't have too much trouble setting something up. Many temple stays are free, though it is polite to make a donation when you disembark - call it good karma.
I find that I get so much more out of a trip when I'm an active traveler, and not a passive observer. Spending a night or two in a temple is a great way to learn a little about a world so far removed from my own.