Wikipedia
The Homomonument is a memorial in the centre of Amsterdam, the capital of the Netherlands. It commemorates all gay men and lesbians who have been subjected to persecution because of their homosexuality. Opened on September 5, 1987, it takes the form of three large pink triangles made of granite, set into the ground so as to form a larger triangle, on the bank of the Keizersgracht canal, near the historic Westerkerk church. The Homomonument was designed to "inspire and support lesbians and gays in their struggle against denial, oppression and discrimination." It was the first monument in the world to commemorate gays and lesbians who were killed by the Nazis.
Later, similar monuments were realised in a number of cities all around the world.