Masso Gastaldi, Glacial erratic in Pianezza, Piedmont, Italy.

Masso Gastaldi is a glacial erratic 14 metres high, 16 wide and 26 long, with a volume of about 2,000 cubic metres, standing on Via Masso Gastaldi just outside Pianezza's historic centre. A relatively recent apartment block is built against its north-western wall. On its summit stands a small unconsecrated chapel dedicated to the Archangel Michael, reached by a staircase cut into the rock, with a plaque to Bartolomeo Gastaldi placed by the Club Alpino Italiano in 1884 below the chapel facade.

The boulder was transported by glacial movement during the Mindel glaciation period through the Susa Valley to reach its current location. Over time, the site evolved to serve religious purposes and later was adapted for military use.

The summit chapel is dedicated to Archangel Michael, a Christian overlay on a site probably used for pagan cults before Christianity. The chapel fell into ruin and was rebuilt as an unconsecrated tempietto reached by a staircase cut into the rock. The boulder is also called Pera Mòra in Piedmontese.

The boulder stands on Via Masso Gastaldi, a short walk from Pianezza's historic centre, with a condominium built against its north-western wall. A staircase cut into the rock leads to the summit chapel; access to the top can be arranged through the Pianezza section of the Club Alpino Italiano. The World War II air-raid shelter, entered from a passage cut at the south-eastern corner, reopened to visitors in 2016 through the municipality and the local CAI.

Hidden within the rock is a World War II air raid shelter that was carefully restored and opened to the public in recent years. This underground space shows how the stone formation has served as refuge for people across different periods of history.