Old Recluse's cave was a cave on the planet Morishim known to be inhabited by the Old Recluse. The cave was in fact a secret Imperial communications center.
The Old Recluse's cave was located in the High Tatmana. It contained a fully functioning Imperial communications center: encrypt/decrypt modules, input jacks for a variety of droids and sensor feeds, a space/planetary monitor module, and a self-contained Generations III power generator.
The communications center was set up before the Imperial forces evacuated the planet in 17 ABY. The cave was inhabited by the Old Recluse, an ancient Morish and Imperial spy. He used the cave's equipment to act as a kind of prophet in order to impress and indoctrinate the Morishm population. He also spied the neighboring New Republic Starfighter Base.
The trick was discovered by Lando Calrissian when he went to the cave with Wedge Antilles, Tycho Celchu, and Wes Janson to listen the story about the Caamas Firestorm. He smelled and recognirzed the odor of the old electronic equipments.