An annual event commemorating those LGBT people lost in the Second World War, the Pink Triangle Installation takes place at the summit of Twin Peaks, and is said to be visible from 20 miles away. Anyone can show up to help construct the triangle, and stay for speeches and a ceremony that usually draws a good crowd and some heavy hitters from the political community (last year the keynote speaker was SF Mayor Ed Lee). Both are free.

thepinktriangle.com