Formerly known as "Swim through Walls", "Phase Swimming" allows you to pass through walls as after exiting first person on the US version of the game as long as the kong and the wall are oriented in certain ways
Swim up to a vertical wall and while underwater, press C-Up to enter first person mode. Line yourself up perpendicular to the wall. Then press and hold A without moving the joystick to exit first person mode and swim through the wall. If you can't get through, try facing a little bit further to the right. This trick does not work with every wall, please read the Technical Explanation below to understand why.
Training Grounds Escape
After beating Cranky's swimming training barrel, go to the left side of the small lake by the tunnel leading to the closed gate. Use phase swimming on the wall on the left, but stay close to the surface and the ledge that drops down to the water. After clipping, keep holding A until the screen fades out. You will end up in the DK Isles main area.
You don't need to play the bongo to open the gate that blocks the way to Lanky's room. Drop into the lava and phase swim through the gate or wall leading to Lanky's cage.
The player's Y rotation (facing direction) is stored as a 16 bit integer meaning the values can range from 0 to 65535. The values between 0 and 4095 represent a full circle in game. When the angle exceeds 4095 the game normally subtracts 4096 until the angle is between 0 and 4095.
If the player is facing between 0 and 2047 and leaves first person mode, the NTSC-U version of the game adds 4096 to the player's angle causing it to be out of normal range. Angles greater than 4095 allow the player to swim through some walls and force the camera to rotate around the player in strange ways. If the player adjusts their angle using the joystick the game corrects the mistake by applying the fix mentioned above for angles that are out of normal range. The game sets the incorrect angle for a single frame while on land, but quickly corrects this by applying the fix.
The PAL and Japanese versions of the game do not incorrectly add 4096 to the player's angle under these circumstances however forcing angles over 4095 using cheats on these versions replicates the glitch with the exact same properties as the US version.