The cache is found about 100m onto the island. It is big enough for several trackables and swaps.
You can check the tide times by looking at this website. If you get the times wrong you can easily be stranded on the island, or swept away by the rising tides on the causeway! There is a noticeboard at the start of the causeway where you can make final check that you are walking at the right time.
You can, apparently, also text CRAMOND to 81400 to get crossing times.
The difficulty rating reflects that fact that you have to look up the access times beforehand. The cache should be extremely straightforward. There is a spoiler picture on this page to make it even easier. The terrain rating is mostly due to the fact that it's awkward to get onto the causeway, and you'll have to walk about 3km round trip.
If you'd like to place a cache in this series, you are most welcome. There are just a couple of points to note:
1. Email den sure kalkun about your cache before you publish it. He will allocate a number to you.
2. Then let him know when it's published, and he'll add it to the bookmark list.
3. The island must be an actual island. Places with the name "Island" or "Isle" that aren't actually islands are not allowed. Any island is ok: sea, river, lake. It doesn't have to be a named island.
4. Only one "Island Treasures" cache per island. Sorry if your favourite island is already taken :)
5. You can place any type of cache in this series (Earth caches are particularly encouraged!) but the final container, if there is one, must be on the island.