There is only one easy way to access the beach where you need to go: take a drive to Flic-en-Flac and follow the road south. This is a dead-end road so you cannot access it from Tamarin. There are resorts all along this road but at the given Parking coordinates you will find a small parking lot with access to the beach. The bus route ends at this point and there are public toilets and showers here, which will come in handy after your dive.
Walk to the beach and head north, crossing the little stream. At the given Reference point on the beach , look out towards the reef. You will notice some drums floating in the water, roughly at the published coordinates. All the drums are attached by chain to a heavy track chain on the seabed- except one, which is attched to a tyre. It should be roughly at the published coordinates, but rather focus on the fish and the corals than your GPSr! The water is shallow all the way, probably not deeper than 1.5 meters at the most. Beware of sea urchins here, rubber booties or flippers are highly recommended if you plan to walk or step on the sea floor! Find the drum with the tyre attached and memorize what BRAND OF TYRE it is! It may be necessary to wipe some sand or algea off the tyre and of course -you do need goggles to see under water!
To get your coordinates you need to get a numeric value out of each letter of the tyre brand. A=1 B=2 etc If the numeric value is higher than 10, take the sum of the two digits, i.e. K=11=2 L=12=3 etc
The cache coordinates are:
S 20° 18. (value of the third letter minus value of the first letter) (value of the seventh letter plus value of the fifth letter) (value of the second letter plus value of the fifth letter)
E 057° 21. (value of the fourth letter plus value of the seventh letter) (value of the sixth letter minus value of the second letter) (value of the second letter plus value of the sixth letter)