Unjusa is a mysterious temple whose precise founding date, circumstances, and founders remain unresolved to this day. Several founding legends have been passed down — that it was founded by Master Doseon, that it was built by a figure named Unju, that it was established by the old woman-deity Mago — but of these, the legend crediting Master Doseon is by far the most widely known. According to this story, Doseon sought to build a thousand Buddhas and a thousand pagodas in a single night, and as the construction neared completion, he moved to raise the final reclining Buddha into a standing position. But at that moment, a young novice monk, exhausted by the labor, lied that the rooster had already crowed, signaling dawn. Because of this deception, the final Buddha statue was never raised and remains lying down to this day, according to the legend.
The relics that survive at Unjusa today comprise 21 stone pagodas and 80 stone Buddhas. Scholars generally believe this temple was not the product of a single sponsoring authority — a state, a religious order, or a wealthy patron — mobilizing large-scale labor, but rather the accumulated work of countless ordinary people, each hoping in their own way for rebirth in paradise. For this reason, Unjusa is often interpreted as a symbol of the Goryeo-era popular faith (popular Buddhism). The fact that, despite no one being able to say with certainty who built this temple, nearly a thousand traces of Buddha statues and pagodas remain here regardless, is itself the temple's most powerful story.