This map allows you to build close to the sea - although actually you cannot get right to the coast, with careful landscaping, lots on the beach can appear to be on the seafront.
This second picture shows how the grid works. This is one of the places Sims 2 does not compare well with Sims 1, where we certainly could build directly on the waterfront (remember Lot 8?). With Bon Voyage it seems we can at last build directly on the sea edge. Hooray!
I used this custom terrain in Sims 2 with a Desert terrain, and it looks like this with a little decoration and some houses, and even better ingame.
How to use a custom Neighbourhood Terrain
Here's the Hood showing a few lots there.