To complete the ancient aqueduct tomb in the Hidden City in Shadow of the Tomb Raider jump into the water and use the lever to lower the water level.
Kick the raft until it is in front of the door and use a rope arrow to attach the door to the raft.
Climb back up to the starting area and use the lever to raise the water level back up. Swim through the now open gate and follow the passage to the next area. Lower the water level using the lever on the wall. Use a rope arrow to clear the rubble. Go back to the first area and kick the raft to the new area. Go back to the start and use the lever to raise the water level and swim back to the new area. Use the raft to climb up, make your way around to the upper area and use the lever to raise the water level. Wait for the raft to float around a bit then stand on it and use a rope arrow to attach the raft to the turning beam ahead.
Sail with the raft to the platform with the turning beam and climb up to it. Use a rope arrow to attach the turning beam to the pulley and jump back down into the water.
Swim over to the raft and use it to climb the middle pillar. Jump over to the weight and then to the upper area of the ancient aqueduct. Go around to complete the ancient aqueduct tomb.