We named this tiny, uninhabited island after my 2 daughters and their 2 cousins, after we all sailed to the island and spent a few hours swimming and sunbathing. We just had to go back and leave the cache!
MATS Island, for Marissa, Allie, Thomas and Selena, is actually called Arbutus Island and is just off of Hermit Island in Howe Sound. MATS is tiny - about 350 meters around - and is a great place to go for a picnic, although there are no facilities and you're unlikely to encounter anyone else there. You can readily kayak, sail or motorboat to MATS from Gibsons or the neighboring islands.
At low tide MATS and Hermit Islands are joined by a thin sand bar, so don't sail or motor between the islands as you could run aground. There is a beach on MATS that you can land at that is only meters from the cache coordinates.
Before venturing out it would be wise to enter the coordinates into Google Earth to actually see the cache location and beach landing spot.
The terrain rating is 5 only because you have to take a boat to the island. Once on the island, the cache is an easy find.