Entering "Neptune's Hall"

And again run to the triggers in the middle. Now it's time to step onto the Waves Symbol to open the next three doors. Here you will find the correct lever behind the left door. - Again the second door is bearing the waves symbol as an indication of where you have to go. - Use the lever and through the gate which opens in the middle passage you can reach Neptune's Hall.

Neptune's Hall

Enter Neptune's Hall. Careful, here you will find a skeleton, that will throw thunderbolts at you. Avoid the thunderbolts and collect the Ammo on the other side. Find the waterhole and dive down into a passage, dive through the blades. There you will find a lever. Use this lever to raise the water level somewhere else. Dive back out and up the passage. Run back to the main shaft and jump into the water there. Search for the passage right of the stone face. Dive into the chamber and use the lever to let in more water. Dive back outside.

Goodies:
Now you have to climb into the passage above the stone face. Run into the passage on the left and collect a large medipack. Return outside. Dive into the passage right of the stone face. In there you can find some Ammo. Again return outside.

Diving

Swim to the passage left of the stone face and climb out. Run over to the left. Dive down into the shaft at the end and follow it. Collect a large medipack on your way. At the end you have to dive further down. There you will find another large medipack. Dive through the opening in the grate and up to the air hole. When your lungs are full again, dive down and further into the other direction. Here you will meet a couple of nasty traps. Dive carefully ahead to spot them and avoid them. Dive through the grate and further past the traps, till you reach a crossing with one path leading to the right and one to the left. At the entrance of the right passage you will find Ammo. Dive to the right and up to the air hole to catch some breath.

Water Crystal

Now follow the other passage get in a chamber underneath the grabe in the main shaft. Collect the Water Crystal from the pedestal. The grate above your head opens, when you pick up the crystal. Dive straight up to catch some breath. Dive back down and use the lever at the column. This will open the gate with the stone face. Dive up and through the gate to emerge where the first lever was. Dive up and climb out of the water. Run towards the gate and return to the Hall of Seasons.