Divers

Run ahead to the water. In front is a giant Neptune statue. Indy hints that he thinks it a good idea to attach some explosives to sensitive spots of the statue. Jump into the water and swim towards the Neptune statue. Two divers will appear through a gap they blow into the back wall. Take them out with the harpoon and collect their ammo. Also collect some detonation devices from the crate on the right side. There is more harpoon ammo by a skeleton on the round floor panel below the Neptune statue.

Neptune's right foot

Place one of these on Neptune's right foot, when looked at from behind, to damage him. Get out of the way. Neptune will sway but remains standing.

Turning off the Water

Then dive down into the shaft opposite the statue. At the end you can climb out on the right into the catacombs. Run up the stairs to the top. Step through the doorway on the right. There drop down and use the wheel on the right to turn off some of the water. This will reveal a spot where Indy will be able to attach his whip. After that two baddies will bomb their way through the wall in the right shaft. Kill them. Climb back up and run down the stairs again. Jump into the water and swim back outside.

Neptune's Trident

Find the little platform in front of the still running water and climb out. From there jump up onto the narrow walkway and follow it. Jump to reach the platform at the end and you are back where you started the level. Running jump towards the left and make your way towards the spot where you can use the whip. Swing to the next platform. Run ahead and don't stop or you will drop through the collapsing floor. If you drop into the water here, you have to jump across the gap in your second try. At the end look over to the left towards Neptune's trident. Take a running jump to get there and swing from it using the whip. Jump to the other side.

Neptune's left leg

Run through the columns and there turn right. You have to get past an opening in the floor. Run over to the right and there you'll find a platform at the back of the statue. Use the second explosive there. Quickly jump up into the chamber on the other side, where you will find another well. Outside the statue takes more damage but again remains upright. However a small column nearby is damaged.

Jump into the water and swim towards the pillar. Climb out, onto it. From there jump up onto the walkway on the side. Climb up the vine at the right wall. At the top run further to the right. Run behind the statue. You can see a lamp dangling from the ceiling above the statue. Take out the whip and use it to grab hold. When Indy swings, he knocks over the statue. He drops into the water and finishes the level.