Where did Apollo 11 land on the Moon?

The place is called Mare Tranquillitatis, the Sea of Tranquility: there's no water there, but a plain of basaltic lava solidified billions of years ago, on the near side of the Moon and very close to the lunar equator. That plain is one of the dark patches visible to the naked eye from Earth. The Eagle lunar module touched down there on July 20, 1969, at 20:17:40 UTC, at the coordinates 0.67416° north latitude and 23.47314° east longitude. The crew named the site Tranquility Base, and Armstrong climbed down the ladder at 02:56:15 UTC on July 21.

The choice was engineering before science. For the first attempt, mission planners wanted the most boring terrain possible: an equatorial zone, which simplifies the orbital mechanics of rendezvous with the command module; with the Sun low on the horizon, so shadows would reveal the relief during descent; flat, free of large craters or slopes, and well photographed by precursor probes. Apollo 11 also carried very little margin: the goal was to land and return, so anything that added risk to the terrain was ruled out. The geologically more appealing sites, with mountains and valleys, came in later missions.

From the visit, the Eagle's descent stage remains, along with footprints, deployed instruments, and a plaque. Of what came back to Earth, the important part is the 21.55 kg of rock and soil collected during the 21 hours and 36 minutes the crew spent on the surface: basalts from a lunar sea, the first terrain from another world that could be dated in a laboratory. Current reconnaissance probes have photographed the site with enough resolution to still make out the module and the trail of footsteps.