The massive temple on the Quirinal hill in Rome is now gone, but substantial remains still exist of the twin brick staircases, and the stair-well, down the hill. Unfortunately they stand in the gardens of the Colonna palace, which is not very accessible; and on the other side is the Gregorian University.
However the Gregorian University was only constructed in the early 1930s. A marvellous photograph exists, showing the site under construction. Behind it, clearly visible, is the huge square carcass of the stairwell, and the twin staircases on either side!
The picture was printed by Rabun Taylor in his marvellous article arguing (convincingly) that the temple was built by Hadrian, and the stairwell by Severus. Here it is:
For convenience, here’s an extract highlighting the staircases on either side. The house built into the Roman arches in between is later.
It’s worth repeating one of the renaissance drawings of the same area (by Giovanolli). It is incredible to think this mostly still exists!