Starfleet's major shipyards orbiting Mars, where many famous starships were built.
The Utopia Planitia Fleet Yards are Starfleet's main shipbuilding facility, located in orbit of Mars and in the Utopia Planitia region on its surface. Many famous ships were built there, including the Enterprise-D and the USS Voyager.
The yards are seen in the Next Generation episode Eye of the Beholder, in a memory of the Enterprise-D under construction, and in the Voyager episode Relativity, in which Seven of Nine is sent back in time to Utopia Planitia shortly before Voyager's launch to stop a temporal bomb.
In Star Trek: Picard, the yards were building the fleet of rescue ships for the Romulan evacuation in 2385, with synthetic androids doing much of the work. On First Contact Day of that year, the synthetics suddenly turned on the yards, destroying the ships and killing more than ninety thousand people. The attack led the Federation to ban synthetic life and abandon the Romulan rescue, and Picard resigned from Starfleet.