Here you have a large easy to find cache.
However, as he is a puzzle, he is not so easy to get in to log...
You need to find two other caches first... Lords Locks and Lords Letterbox
They contain info that will allow you to firstly find the cache location, and to be able to access it.
You must sign the log to claim this as a find. There is a log inside, you just need to get in and sign it!