This cistern is an interesting example of a rainwater deposit, with stone vaults resting on pillars and measuring 15m in height and 10m in width and length. It was used to collect and store rainwater to supply the monastery.

Similar in age and location to the cistern, during the Civil War the coal cellar served as an air-raid shelter for the teachers and pupils at the centre, as well as for the neighbouring population. It was particularly suited to this use because of its construction, with barrel vaulting and very thick walls, cut partially into the rock itself.