Lemnos was a mountainous area in ancient times, believed to be the capital city of the Tochika tribe. This is likely the "town" that you visit in Monster Rancher 3 where Bragma lives. It was once famous for its floating shrine.
Lemnos is mentioned in Monster Rancher 2 when Dr. Talico sees the giant Phoenix statue erected in some ruins near the Kawrea Volcano. He is overjoyed when he suddenly realizes that you may be standing in the remnants of the lost Lemnos Shrine.
Sadly, much of the land that made up Lemnos was lost in the cataclysmic events of the continental divides. It is possible that it is now underground, and could be the area that Moo uses as a base in Monster Farm Lagoon.