Air B'n'B has a new app called "Discovery" where you can find all kinds of quirky places for short-term stays like house boats, windmills, buses, and private islands.  Included in this eccentric mix are tree houses which are fast becoming the most popular of the bunch. 

Re-awaken your inner child in this cozy tree house located in San Francisco with a view of the Bay and Devil's Island.  Perched above it all in a quiet, forested canyon, this quaint retreat is equipped with everything you need: a double bed, French doors, stained glass, a hand-made quilt, a private swing, and a wrap-around veranda where you can soak in the views.  Wondering where all of the plumbing is?   Not to worry - the main house is only a stone path away where you have your own private washroom and kitchenette.

Tree House Above San Francisco Bay
Sleeps 2-3 | $235 / night