Start off by heading straight for the ramp with the 4 second boost and then right to the ramp with the 9 second boost. The track takes you on a long left with a 4 second boost on its inside. You could collect this boost and then continue on to the ramp ahead with the 4 second boost and the checkpoint. Alternatively, as you land from the ramp with the 9 second boost, you will find a banked rim to the right of the track which is just big enough to fit your boat on. Keep your speed up by jumping and land on the banked turn and slide your way to the ramp with the 4 second boost. Either way, ignore the annoying Greek Police boat - you're about to leave it behind.
After the checkpoint, look to the left for a waterfall. Drive straight under it using your boost to ensure no boats knock you out of the way. On the other side of the waterfall you'll take a left and a long sweeping right-hand turn with a pair of 9 second boosts along the way. About four curves after the second 9 second boost is a waterfall off of which you drop. Try to be in the middle of the track and don't use a boost. As you drop off, look to the left so you are ready for the landing. If you positioned yourself correctly at the top, you will collect the 4 second boost at the bottom and if you've oriented to the left while dropping, you'll be ready to boost yourself from a stand-still along the pillars that will be on your right.
After the pillars there's a 4 second boost in the air. This one is only worthwhile if you are already running low on boost. Immediately after the boost is a slide down to a flooded coliseum and another ramp, this time with a 9 second boost at the top. As with other slopes, there's no need to boost down this one so you can conserve boost if you need to. Boost on through the 9 second boost and you will land just short of a tunnel. Part way through this tunnel is a waterfall on the right-hand side, which you have to boost to get up to and there's a 9 second boost at the top. Don't bother getting it though, as it's not worth it. Keep going straight and collect the 4 second boost instead. At the end of the tunnel you'll drop into a cavern and a 4 second boost lies in front, as does the exit of the cavern.
Out of the cavern you'll go under two archways and the second has a bridge of some kind immediately after it. Get ready to jump as there's a 9 second boost hanging in the air just after the bridge. You'll now be in a canal which leads left then right and is great for using a boost jump to jump over the right-hand side, even though it's tight as the invisible wall stops you. Carry on straight, collect the 4 second boost and you'll be going under another series of archways/bridges. You will pop out the other side on a long sloping part of the canal with various archways along the way. Again, as with other slopes there's no need to boost down this, though you may like to near the top to get the speed up to max earlier. The slope goes right, left, right and then straight to the bottom.
At the top of the slope you'll be able to see the finish line, so when you've got to the bottom, boost through the 4 second boost to the ramp and you should be able to fly your way to the finish line.