Inspecting the statue in the water,
Jack notices there is something underneath the statue. I'm assuming
Elwood will help by bringing his glowing shield over to light up the area beneath the statue. Doing so reveals a short skeleton in rusting armor. Your best guess is this was a kobold. You might be able to tell for sure if you remove the statue and pull the skeleton out of the water for a close inspection.
Jack and Elwood do not see anything unusual in the alcove, certainly not any sign of a secret door or passage. The ground between the alcove and the statue's feet is undisturbed and not interesting in any way. The statue's feet are carved to depict metal boots that fit with the plate armor (recall the entire statue, including what it is wearing, is a single piece of carved stone).
Seline's ability to inspect the east wall for secret doors (or other noteworthy features) is somewhat limited by her inability to get close to the wall. If Seline is willing to get wet (or comes up with a way to get to the wall without taking a dip in the stream), she will be in a much better position to investigate. For now, she is not able to detect anything in the east wall. The statue does not serve as a bridge to the east wall since its head and torso are submerged. You cannot reach the ceiling without doing some climbing or employing magic (it's a good 15 feet high in this chamber).
Things take a turn toward the dramatic when
Jack approaches the next alcove. He does not see any signs of a secret door in the second alcove. However, as he begins to walk past the second alcove, the statue in that alcove springs to life. In a flash, it lunges out of the alcove and tackles Jack. The fighter manages to retain his balance just at the edge of the stream. It takes all of Jack's strength and agility to avoid being shoved into the water.
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15:58, Today: Castle Keeper, for the NPC Statue, rolled 20 using 1d20+10. Overbear Jack.