Crowning the Praça da Sé is the domed Catedral da Sé, a huge neo-Byzantine concoction that, for better or worse, replaced the original 18th-century structure in the 1920s. Still, its stained glass and mosaic interior is worth a gander.
The steps leading up to the cathedral are a popular loitering spot for mostly harmless vagabonds – just stroll on by and you aren't likely to be bothered. If so, police frequently patrol the square.