Mearls had a high level adventure in Dungeon maybe a year and a half ago that involved the PC's entering a titanic living, evil tree infested with a hag druid and her T-Rex companion.
The tree was sentient, and would spray sap/acid on the party, constrict its chambers at inconvenient times, etc.
Good adventure too. Can't recall the name for the life of me though. I'm at work and don't have my books.