Cache is located just at the end of the tidal causeway on Cramond Island. Before attempting to go to the final location, it is necessary to check the tides and make sure it is safe to cross: see below for more information and remember that you are going to be tested at the end!
Safe crossing is from two hours before low tide at Leith to two hours after low tide; in other words, four hours starting two hours before low tide. Tide tables for Leith can be obtained from many sources, I personally use these which I find reliable.
There are also two notice boards near the start of the causeway which contain the safe crossing times already worked out for you: there are two additional waypoints with the location of these notice boards.
Now on to the cache. You'll need the following information:
The duration of the safe crossing period, in hours; let this be S
The number of notice boards containing safe crossing information, for which I provide waypoints; let this be N
The number of caches this page describes; let this be C
The above coordinates, which are the middle point of the tidal causeway, are N55°59.170 W003°17.?81; let the missing number be Z
The cache is at N55°59.SCZ W003°C7.SZN.
Safety notice: do not enter the building; the big red "Dangerous Building" signs are there for a reason.
For a full explanation of tides, please see Jaumet's earthcache GC3XNMG, which you can also do while on your way to (or from) this cache.
The cache meets the GAGB Urban Placement guidelines.
The cache has been placed for the Cramond Welcome event on 21/7/2012 and cachers were asked not to look for it until 8.30 on that morning; congratulations to Ronaldshay Rumagers and AJ45 on their joint FTF at about 8.47am!