Either this was not a Christian Chapel, or it had been adapted to her own purposes by the sorceress Hellawes, Lady of the Castle Nigramous, who "ordained" the chapel to entrap Lancelot or Gawaine.

Riding in a deep forest, Lancelot followed a black brachet which was tracking a feute of blood. The brachet led him over an old, feeble bridge into an old manor, where he found the body of Sir Gilbert the Bastard, with his wife grieving for him. Leaving the manor, Lancelot met a damsel he knew, who told him that her brother, Sir Meliot de Logres, had fought and killed Sir Gilbert that day, but had been wounded himself. The bleeding could not be staunched, and Meliot could only be saved if his wounds were searched with the sword and a piece of the bloody cloth wrapping the dead knight in the Chapel Perilous.

Lancelot proceeded to Chapel Perilous, on the front of which he saw many fair, rich shields hanging upside-down. Thirty armed knights barred his way, grinning and gnashing their teeth at him; when he resolutely stepped forward, they stood aside and let him pass. In the chapel, by the light of a single dim lamp, he found the body of Sir Gilbert lying covered by a cloth of silk. When Lancelot cut off a little of the cloth, the earth seemed to quake. When he came back outside, the thirty knights threatened his death if he did not lay down Sir Gilbert's sword, which he had picked up in the chapel along with the cloth. Again Lancelot passed resolutely and safely through their midst.

Next he met Hellawes herself, who first threatened his death if he did not lay down the sword, then tried to get him to kiss her once. When he refused, she confessed that either to lay down the sword or to kiss her would have cost him his life. She had been in love with him for seven years and, despairing of his love, had hoped to have his dead body to kiss and fondle. She had had Sir Gilbert and cut off his left hand. [Had Hellawes been less lethal with Gawaine than with Lancelot because she did not despair of winning Gawaine's carnal love?] Proceeding from the chapel, Lancelot healed Meliot. Hellawes died. I do not know whether Sir Gilbert was Hellawes' unwilling accomplice or unwitting tool.

The Chapel Perilous would appear to have been in one of the Forests Perilous.