Sentinel Beach is a location in Jak and Daxter: The Precursor Legacy. One of the first places Jak and Daxter visits. The beach is located around a large bay with an old tower at the sea-mouth and some old stone sentinels at the end of the beach. Several Lurkers live in this area, both on the beach and the higher grassy area, once inhabited by people but now seemingly abandoned.
The Precursor Legacy
Sentinel Beach was one of the first areas Jak and Daxter visited in The Precursor Legacy. It was also in the first mission that the duo receive, in which Samos told them to reactivate his Green Eco harvesters (in Unblock the eco harvesters). They later do many more missions, some unlocked just as individual exploration (such as Get the power cell from the pelican), but others can be discovered by talking to residents (such as the Birdwatcher's mission Push the flut flut egg off the cliff).
Sentinel Beach is a beach expansion of Sandover Village to its west, which can be reached by going under three arches. It features a few houses and a Lurker constructed Cannon that is located on top off a fortress out into the sea. The area has three stone Sentinels that do not seem to serve any purpose and also a bunch of Green Eco Vents which Samos is using to farm Green Eco. The area has a large waterfall and a bay, with a small island in the middle of it and an three stacks with precursor launchers on them which can be used to access the cannon tower.
The area also features a flut flut egg which is closely being observed by the Birdwatcher. You can find Green and Blue Eco here. Both have Vents and there are also Launchers. Other birds include a swarm of seagulls and a lone pelican.
The beach is also home to the Sentinels, the cliffs containing the Green Eco harvesters, and some windmills. One soldier lurker is operating the Cannon, though it can also be used to kill any of the Lurkers roaming around.
These strange stone structures can be found at the back of the area, with two soldier lurkers roaming around. One has partially collapsed, this is not the Lurkers' doing as the blocks that have fallen in the sea as a result of this have plants growing on them.
When Jak, discovers these Sentinels, they are mostly just serving as a resting grounds for seagulls. Daxter suggests to scare them away, leading to an avalanche which reveals two Precursor Robots. On the reverse side of the partially ruined sentinel there is a small room which could have been a courtroom. This could have been from the early builders of these Sentinels.
The partially collapsed Sentinel has a scout fly resting on top. The centre strucuture has five precursor orbs passing through its top arch and the far Sentinel has a power cell resting on top. This is the power cell which you can see in the cinematic towards the beginning as Keira notes: "I bet there are even more of them out in the wilds, just waiting for some brave adventurer to find."
These Sentinels are possibly early structures created by the Precursors or another race (possibly humans as it resembles no precursor artifact currently known and they are made from grey stone, not Precursor Metal).
Lurkers have constructed a Cannon on top of the fortress structure, which can only be accessed by Launchers. Its range doesn't go any further than the bay area and it fires pretty slow. It is unknown why, but perhaps it was placed there to destroy the Metal Boxes, it would also have been useful for capturing Samos as he checked on his eco collectors or perhaps to start up another Lurker base.
Though the area, at first, was pretty much devoid of any Precursor artifacts besides the few Vents and Launchers, it actually contained quite the beautiful view. Once one would scare the seagulls away, leading to the avalanche and showing the immense two robots standing beside the waterfall. It is unknown what happened to these graceful statues in Jak II, sadly.