Reptite Lair is a location in Chrono Trigger that appears in Prehistory. When Kino steals the Gate Key from Crono on his quest for Dreamstone, the device is stolen by Reptites and brought to Azala at her base in the Reptite Lair.
To get the Ruby Vest you have to make the Aecyto Weevils follow you until the right side of the first room, then they will penetrate the soil and will give you the access to the room where is set the chest with the ruby vest inside.