I located the clue from an online treasure locater off tip.it and it said the clue was in tirannwn. I was wonder if the underground pass quest was the key to unlocking that area. If not, then please tell me whatever I need to do to gain access to that spot. Thanks!

u must have done undeground pass and start regicide

Gooz is right. You need to at least start Regicide and have at least 56 agility to get to that area. You don't need to finish Regicide, but it helps if you do. And yes, you need to finish Undergroud Pass first. Having finished Underground Pass is one of the requirements for starting Regicide.