Hydro Thunder/Lost Island
Begin with a super boost and head straight for the ramp that's immediately in front, picking up the 4 second boost. The track takes a right and you'll see a waterfall ahead while the main track veers left. Go under the waterfall and pick up the 9 second boost as you glide left and the next 4 second boost off the ramp at the end. It's a good idea to perform a jump off the end instead of relying on the ramp as you'll travel farther before rejoining the main track below.
As you join the main track again, look to the left. You'll see a series of huts here followed by a rocky outcrop and then an archway straight ahead. As you join the main track a host of arrows will fly above your head. Use your boost to get between the second hut and the rocky outcrop. You're now in a secret tunnel.
Once in the tunnel, go headlong to the 9 second boost and left to the checkpoint. Shortly after, head right to a 4 second boost, then right again out of the tunnel to an elevated section just off the main track below and to the right of you. Collect the 4 second boost and, keeping on the elevated section, head short right then left to another ramp, aiming for the 9 second boost that is just after the ramp. You'll drop back down to the main track.
The main track takes a sweeping right passing the next checkpoint and a 4 second boost. A series of gangplanks make up a sort of quay just above the track - be careful not to jump straight into one or you'll lose control of the boat very easily. Carry on through the archway and down the dip of the track which takes a left here. There's a long straight here where you can do some hydro jumping and get your speed up. It ends in a waterfall down away from you - there's a bridge just after it and another waterfall on your left. Ignore the waterfall on your left, but if you can catch the top of the bridge it'll keep your speed consistent for a bit longer and prevent you from hitting the water. Head straight for the 4 second boost ahead and enter the tunnel.
After entering the tunnel, the track heads right and enters a cavern with a ramp and volcano ahead. Use the ramp to jump over the volcano and pick up a hidden 9 second boost. On the other side of the cavern (straight ahead from the ramp-volcano jump) is a 4 second boost. Another right turn and then a drop into another cavern leads you to a skull-capped archway. Under the archway you can see the finish line.
Keep to the left side under the skull archway and head for the ramp and the 4 second boost ahead. Boost your way to the finish line.