In reply to Fiskavaig:
Where is it, England, Wales, NI or Scotland and Is it an existing crag that has been neglected or a new venue?
Could be a developed crag whose status/access has changed and thus not visited and now overgrown.
Worth contacting the relevant governing body eg BMC, MCOS (MS) or other to see what the access status is and to let them know of your intentions.
Then follow it up with a call to either English Natural Heritage, Scottish Natural Heritage etc to see what status the area is classed as and if there are any restrictions.
And as others have said, get some help and good luck!