Get through the Lurker fort was a mission that Jak and Daxter completed to obtain a power cell in The Precursor Legacy. After opening the gate to the fort, Jak made his way through several obstacles to grab the power cell within.
There are two ways of carrying out this mission. The way that it is meant to be done is by climbing the tower and jumping up the wooden platforms to eventually end up on a large structure in the corner next to the entrance. Then you must work you way around the edges of the fort on the thin pathway made for this mission. There's some slippery platforms, poles and moving platforms as well as a couple of ice citadel bunnies. Half way round, there is a wooden pillar which you activate by pressing a nearby button. From this point, if you fall you may use this pillar to return to the half-way point. At the end you'll find a power cell.
It is also possible to abuse the range of your long jump and simply launch yourself to the power cell's structure from the tall watchtower. Similar shortcuts can also be used to reach the midway point.