Five entries with the name Perilous Castle.
Perilous Castle
A manor where Sir Meliot of Logres lay sick until he was cured by Lancelot.
Perilous Castle
A castle Arthur had to conquer in order to free the Kingdom of Damsels from the grip of a tyrant.
Source
Le Chevalier du Papegau | Late 14th century or early 15th century
Perilous Castle
Chastel Paorous
A castle ruled by Lord Menelais.
It was said that no one passed the castle without seeing or hearing something that would terrify him.
Source
Meriadeuc or Le Chevalier aux Deux Épées | c. 1225-1250
Perilous Castle
A castle ruled by Orgueillox the Proud.
The castle’s enchantments were destroyed by Arthur’s knights Claris and Laris.
Source
Claris et Laris | 1268
Perilous Castle
Tristram (Tristan), Gouvernail, Kehydius, and Dame Bragwaine (Brangain) were on their way by boat from Brittany to Cornwall when an extremely “contrarious wind” blew them off course to North Wales, where they came ashore near the Castle Perilous. Tristram went into the forest because
in this forest are many strange adventures, as I heard say.
This would seem to put it near the Forest Perilous of Annowre the Sorceress in North Wales.