Craig Y Castell is a crag that runs above the Onnau valley (Cwm Onnau) that sits above the main Usk Valley. Behind the crag the moor turns into Mynydd Llangatwg (Llangattock mountain) that sweeps to the south and to the Welsh Valleys.
The Cache
This is an extreme terrain cache on a vertical cliff face and is only for those cachers who are experienced and competent with climbing/abseil equipment.
When I placed the cache I approached from the car parking waypoint and went round to the right (west) of the crag to an obvious path where there is a break in the rocks that leads to above the crag. I walked to above the cache spot then and abseiled down.
So here's the safety bit - just because I have placed the cache on the crag does not mean that that crag is safe to climb or descend, only that I was happy to do it when I placed it. If you arrive at GZ and you think it is not in your capabilities to get up or down with the correct equipment (and/or not know how to use it!) then walk away - the decisions to climb/abseil (and therefore the consequences) are entirely your responsibility. Please also remember that rocks can move or become loose over time, rain will make things slippery and winds will increase the difficulty/danger.
Having said all of that I had great fun setting this cache!
In addition, to earn the D/T rating, this cache should only be claimed as a find by those who actually go down the face and lay hands on the cache itself rather than just one person in a group and everyone claims a find (although I can't verify this of course so I am relying on your honesty here 
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I reiterate - the fact that I have placed this cache here DOES NOT mean that I am saying that it is safe to attempt when you are there - that is entirely up to you to decide and I can take NO responsibility for your actions or safety should you choose to attempt it. (So please be careful 
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The cache is a small tobacco-type tin in a camo bag. I have secured it with a peg so if it does come loose when you are retrieving please re-secure as this is obviously relatively difficult to maintain.
Many thanks to Knight Frank for permission for the placement of this cache.