I really love forts. And since I'm such a flexible toddler-peep, I define fort loosely. It's more fun that way. One of my favorite forts is Sissy's kennel. It's a great spot to read books.
My other favorite fort? Laundry baskets! I love playing in laundry baskets, especially if they're filled with cozy toasty clean laundry. And yes, sometimes I need to fling around the folded laundry to get situated. (Mom thinks that's lame.)
Even Elmo loves laundry baskets.