Outpost L51 was an outpost on planet Sargasso. Possibly built to harvest Gelatonium, the outpost was visited by Ratchet in his search for the elusive "Lombax secret". Surrounding the outpost was an unforgiving swampland, infested with many creatures, such as Grunthors.
Ratchet "met" many Kerchu working at the outpost. It is unknown if these Kerchu were employed or were the builders of the Outpost - although they were likely the builders, as a news report during the Nefarious Time Crisis suggests.
There were a few Robo-Wings pads scattered around the area, although their purpose beyond Ratchet's exploration is unknown.
Ratchet did not find the Lombax secret here, since it had been re-located by Max Apogee. Instead they did met the Plumber, who was building his new transportation device (a giant toilet). The plumber gave Ratchet and Clank the 3 ¾ Centicubit Hexagonal Washer, a device that would ultimately save the duo's life.