The U. S. Army built this powder magazine probably before America's Civil War. Because its purpose was to store gun powder, the walls are made of stone, three feet thick. If there were an accident, the roof would blow off, but the blast would not level neighboring buildings . . . and people.
Nowadays, it's a historic building in the Presidio of San Francisco, the only part of the National Park Service that is self-supporting. The Presidio Trust rents out the buildings left behind when the Army closed its base in 1996 to pay the costs of maintaining it for all to enjoy.
Inside the building is a sculpture by Andy Goldsworthy called Tree Fall, one of four Goldsworthy sculptures in the park (See below). This one uses the windowless one-room building to create a mysterious atmosphere for a section of a eucalyptus tree, which seems to float overhead. The tree and the ceiling are coated in clay, making it seem we are underground.
I have the pleasure of welcoming visitors to Tree Fall and the park two or three days each month.