parkerjason: been upto see this today,,and unfortunately it has been sealed permantly with metal doors. i was then intending to leave it available ,but with an abseiling attribute,but unfortunately new grids have also been attached to all 4 air shafts,making the whole tunnel un attainable.
so i have no choice but to archive this cache,many many thanks to everyone who attempted the cache.
i will replace this ,number 3 in the "we all float" series soon.