Made a quick stop here while in downtown Rio (it's not far from the Valongo Wharf WHS). It's the strangest approach to a monastery as access is by elevator from a modern building on the street below (addresses are for that building if taking an uber or taxi) and the security guy points you in the right direction.

The monastery is free though only the small church is open to the public. The exterior is simple and would never suggest one of the most ornate interiors I've ever seen. Despite its smallish size you could spend a long time in there trying to pick out every detail. 

Although it's on a hill in the middle of the city, there are no views and it was surprisingly quiet and peaceful. As this is not difficult to get to, it is a worthwhile quick stop while collecting the other sites of Rio.