Spot just outside the Watertower in Arlington, MA. Gandalf's Cave is marked by bio-hazard graffiti and the name GANDALF"S CAVE spray painted on the large rock. The spot is commonly used by thrill seekers looking get "sauced". If you are looking for Gandalf's Cave, you can look for the burned area and the trees that have been literally kicked down. They say if you get drunk enough you can see Gandalf himself wandering the area.