Two entries with the name Guinas.
Guinas
Guins
A count who sought to measure Gawain’s strength, erected twelve pavilions near his castle and filled them with knights to dispute passage to all passing knights. When Gaheris and Sagramore had each unhorsed one of Guinas’ knights, Guinas’ dwarf told them they were free to proceed, and gave Sagramore a new lance to replace the one he had broken.
Here we see that not all knights who guard passages need to be blood-thirsty scoundrels, nor all such disputed passages mortally perilous traps. Some of the guardians may be sportsmen, and the disputed passages safe (barring accidents) places to pick up glory.
Gareth eventually conquered Guinas and made him promise to surrender to Gawain, and sent him to Gawain as a prisoner. I found no clue to the location of Guinas’ castle. Guinas’ sportsmanship suggest a locale in more settled areas, possibly in territory in or near that held by the chivalrous Duke Galeholt.
Source
Vulgate Lancelot | 1215-1230
Guinas
A lord of a castle whom Gareth fights. When exhausted he falls into the water, dragged down by his armor, and is drown.
Is he perhaps identical with the Guinas mentioned in the entry above?