Things You'll Need
Instructions
Open "RollerCoaster Tycoon 3." Allow the game to fully load. The main menu will appear. Select "Play." A set of game types will appear. Select the game type that corresponds with your playing style. For example, if you would like to complete a set of predetermined game goals, select "Career Mode." The game type will load. The game world will appear.
Press the button labeled "Paths," located on the main navigation bar. The "Path Construction" options will appear. Select the path icon labeled "Regular Path." A list of different path types will appear. Select the path labeled "Underwater Tunnel." The selected path will appear over your cursor.
Locate the body of water that you wish to construct the underwater pathway in and count three tiles outward from where the water begins. Click the third tile to place the beginning of the path onto the selected tile. Click the thumbtack icon labeled "Toggle Path Editing Icons." A list of construction options will appear. Click the arrow labeled "Straight" two times. You path should now be touching the water.
Click the arrow labeled "Downward Slope." Your pathway will begin to descend into the water. Continue to click the arrow until your pathway has reached the bottom of the body of water. Click "No Slope" icon. The pathway will run along the bottom of the body of water. Continue to click the icon until you've reached the other side of the body of water.
Click the arrow labeled "Upward Slope" until your pathway appears out of the water. Click the "No Slope" icon. Your pathway is now completely out of the water. Connect it with other pathways in your theme park.