Instructions
Select the ̶0;New Ride̶1; icon, and then select ̶0;Roller Coaster̶1; and ̶0;Build This̶1; to start building your own roller coaster.
Select the ̶0;Land̶1; icon (a shovel digging into dirt) when you̵7;ve reached the part of your track where you wish to place a tunnel.
Click a tile of land near your roller coaster. Move your mouse upward to raise the land upwards and create a hill. Continue this process until the hill is as long as you want your tunnel to be.
Click the ̶0;Track̶1; icon to continue placing track. Place the track through the hill and it will automatically form a tunnel through the hill and come out the other end.