Hi B,
I've got all the clues - and the anagram does indeed spell out Thomas Telford.
The spa was Trefriw Wells.
The village with the church was Caerhun, and the fort Canovium.
So the 'famous person' is Thomas Telford. Is the 'town' where the trail ended Menai (if it is a town)? But, it has to link with the besieged and refuged kings. There is a Penrhyn Castle nearby ...
Notice the reference to 'we have already met fellow treasure-hunters there' - as Menai was a previous answer to this competition.
ADE.,