Site: Roman Wall - Tower Hill (1 memorial)
EC3, Trinity Square, Tower Hill Station
Despite having a light shining on it, the exposed section of wall just looks like a rough black area inside a black hole framed in black tiles.
The plaque is attached to a pillar on the westbound platform of the Circle and District line, at the east end.
Ian Visits has a photo of the wall before the railway line was cut through it in 1882.