One of my favorite things to do after running instances or smaller raids is unwind by find and exploring "secret" locations in Azeroth. I've found the airport in Dun Morogh (sp), the highest mountain point in Azeroth, a hidden village in the wetlands, an eternal abyss that you must use the "unstuck" feature to get out of, and much more.
There's no loot or bosses, no raid needed, just fun exploring and some of the best screenshots I've ever seen.