The monastery does not merely sit beside the cliff — it is embedded within it. The cave forms the rear wall and ceiling of the complex, and the monks have built outward from the rock in successive tiers, adding floors as communities grew and rebuilding when disaster struck. The result is an eight-storey structure that merges seamlessly with the limestone face, its whitewashed facades emerging from the overhang in a way that appears, from a distance, almost geological. The gorge of the Vouraikos below carries a narrow-gauge rack railway — the Odontotos, or 'toothed train' — and from its windows, passengers look straight up at the monastery stacked above the void. The monastery lies about 11 kilometres northwest of the town of Kalavryta.

The monastery's history is a chronicle of destruction and return. Large-scale disasters struck in 840, in 1400, and again in 1640 — each time, the community rebuilt. Through Byzantine rule, through the Frankish Principality of Achaea, through Ottoman centuries, Mega Spilaio persisted. From around 1354, it served as the residence of the Orthodox Metropolitan of Patras, whose city was then under Latin occupation; the cave monastery became a refuge for the authority of Greek Orthodoxy itself. The community that lived here held together an institutional continuity that outlasted every power that tried to eclipse it.

The worst moment came not in the medieval centuries but in the twentieth. On 8 December 1943, soldiers of the German 117th Jäger Division crossed the Vouraikos gorge and reached Mega Spilaio. They accused the monks of sheltering British agents and supporting the Greek Resistance. Twenty-two monks and monastery staff were killed. The complex was burned and destroyed. The massacre at the monastery was part of a larger operation in the region — within days, the Wehrmacht carried out the Kalavryta massacre, killing the male population of the town and burning it to the ground. It remains the worst atrocity committed in Greece during the German occupation.

After 1945, the monastery was rebuilt from the ground up — the most recent in its long sequence of reconstructions. The eight-storey complex that stands today is largely postwar construction, though it incorporates what could be salvaged from what came before. The monastery celebrates its feast days on 15 August, the Dormition of the Theotokos; on 14 September; and on 18 October, the feast of Luke the Evangelist, along with the community's founders. It remains an active male monastery, and its treasury holds icons, manuscripts, and relics accumulated across centuries. Visitors arrive from the road below or by the rack railway, climbing to a place that has been, through every disruption, continuously inhabited.