Yes, it's been very interesting recently Punchbowl.
What you saw from your bus are the foundations of mostly 18th century buildings at James' Gate, before the Wide Street Commissioners got their hands on it. You can see the buildings we have found recently marked in red on the Rocque map extract attached (1756 date).
The walls you saw are actually a mismash of multiple phases of buildings built over each other. The Rocque-phase of c. 18th century buildings are probably the middle phase, demolished c. 1850s. Later on c. 1900 there was a smithy here and we found some of the remains of that. We also found some earlier stuff - in particular one large and deep masonry wall, made of large limestone blocks, without any obvious function, below those buildings. It was quite deep (it was not visible from the bus) so I couldn't get a handle on it, but I've interpreted it as a potential early-post-medieval structural remain possibly associated with St. James' Gate and we preserved it fully below the ground after surveying it.
We also found a large brick culvert running under the buildings, frequently altered during the 18th and 19th century. I think it's odd that this runs under buildings, however the 1848 5-foot OS map does show a watercourse running under buildings near here (albeit further east down the block). Our piece of the culvert was very interesting because it had features such as massive brick piers 1m thick, rounded to assist with water-flow, with areas for sluice gates and other control features. Perhaps part of a mill-race complex, common around here with all the distilleries.
I think it carried a branch of a watercourse that ran down here, across St. James' Gate and down Watling Street. This might be called the 'Glib Water', but I don't think it exists anymore. You can see bits of it on Speed's map of 1610, brooking's map of 1728 (where it defines the boundary of the City of Dublin to the south and west) on Rocque and on the 5-foot 1840s OS map.
Further south from all that stuff beside the bank - under the actual road - we also found part of the watercourse. But this took the form of a very big ditch running E-W along James' Street, so possibly representing the watercourse when it was uncovered. The ditch was backfilled in the c. 13th century and the backfill is packed (literally) with a very dense concentration of medieval artefacts, including large pieces of french jugs, floor tiles, and lovely decorated roof tiles that might be from a (demolished?) local religious building. After the ditch was backfilled (presumably they had rerouted this medieval watercourse first) they packed the soggy top of it with a tick layer of gravel, that sunk in slightly, and seems to have formed the sub-surface of a widened late medieval James' Street similar in width to the current road. This ditch has been fully preserved under the ground and the path of the fibre-optic cable currently being laid here has been raised a little bit so that it does not touch the medieval feature.