At the locality of Costa, above the main hamlet of Murialdo, the ruins of a medieval fortress of the Del Carretto family occupy a wooded ridge with views down the valley. The remains include a keep, a long curtain wall, and two gateways with pointed arches — enough to give a clear sense of the original scale of the fortification.
The castle is accessible by a rough track from Costa. The site is not maintained but is open to walkers. The walk from the valley road takes about 20 minutes and passes through chestnut forest. Good walking shoes are recommended; the path can be muddy after rain.