When standing in front of Igreja do Carmo, we are in fact looking at two churches with a very…read morenarrow house, called Casa Escondida or the Hidden House, between them. The right side is Igreja do Carmo (built 1756 to 1768), a catholic church and is popular for its rococo/Romanesque style with the tile exterior. The left side is Igreja dos Carmelitas (mid-17C) that may or may not be open for visitors.
The neat thing about visiting Igreja do Carmo is that the admission fee provides access to uncommon corners and behind-the-scene places, such as standing at the pulpit, the catacombs with a mummified sister on display (yeah, for reals!), relics (i.e. fingers and bones of saints), a museum, and roof access. The altar is very ornate. A unique viewing point is accessible that may have been a private corner for the very wealthy or royalty. And, I can kiss the foot of Jesus (no, I did not).
The 3-storey Casa Escondida or the Hidden House has a wall-to-wall width that is supposed to be 1 meter wide (according to their website). It looks wider than that. Legend has it that this house was built to prevent contact between the monks of Igreja do Carmo and the nuns in the Igreja dos Carmelitas. The reality is likely less juicy, to fill an unsightly gap. It also housed guests and held secret meetings during the Napolean invasion in 1832.
Definitely recommend seeing this church with the unique access.