Yes, it looks like a prison from the outside and the interior decor is plain to say the least, however in every other respect we found the hotel to be excellent.
We had no trouble finding it at all, Rue Barbacane runs along the bottom of the hill that La Cite sits on, just follow the road from the Pont Vieux (footbridge over river), it's right at the far end of the road.
We had an apartment for 4 and the rooms are huge by French standards,
the kitchenette is well equipped, we didn't cook anything but the fridge came in handy, sofa bed and TV, seperate loo and bathroom and (carpetted) bedroom all very clean and housekeeping changed the towels etc daily.
Rooms can vary with regard to the view, if you get one on Barbacane then maybe not so good, the other side of the hotel looks out over the stream or a inside room over the courtyard/garden, which is what we had (A3).
Location is great, a footpath is just yards away that takes you up hill into La Cite, and to be honest wherever you stay, you will find a hill of somekind to get there! A couple of shops just down the road, a bar 10 mins away - and lots up that hill of course - I thought it was a good excuse for beer after the climb!
The "new" town (dates back to the 1200's!) was very interesting, not so touristy and lots of little streets to explore as well as a square
full of cafes and a thrice weekly market.
The new town is about 15 mins away:
Direct route, left down Barbacane, right into Rue Gaffe the left over Pont Vieux.
Scenic route, first left from hotel, right along the bank of the stream, over bridge, through the park, over the river on the causeway
and right through Bellvue gardens.