Ouro Preto's sights are largely architectural and religious, clustered around the main square, Praça Tiradentes, and along the surrounding hillside streets. The Igreja de Nossa Senhora de Pilar is one of the most opulent baroque churches in Brazil, its interior covered in gold leaf and intricate carvings. The Museum of the School of Mines on the main square houses an impressive collection of 25,000 gems and mineral samples — a fitting reminder of the town's geological heritage. Aleijadinho's sculptures and architectural work can be found in several churches throughout the town.