You may think 28mm is quite wide, it is, but if you have the chance to try a 24mm lens, do so.
I have just come back from Iceland and Germany where I had 24mm, 50mm and 105mm lenses. I used the 24mm almost all of the time. Followed by the 50mm for some of the time, then the 105mm for only a few shots.
I have used a 28mm quite a lot for European city scapes, it works well, but with a 24mm you have quite a bit more flexibility, along with the ability to get the top floor of the many five story buildings in abundance in most of the Europe that I know.
I have a Sigma Super-Wide II f/2.8 24mm lens, takes 52mm filters. Bought new over 30 years ago. They sell quite cheaply these days.
My 28mm is a Nikon Series E f/2.8 and one that is currently on one of my bodies now, it is being used in an urban environment exactly as you suggest. It is quite good after the 24mm only as my wide close-up type lens, but it does not have the ability to get all the picture in in tight places. Takes 52mm filters
I don't run 20mm or 21mm lenses, but I do use an 18mm lens, which is another Sigma lens. It is more than competent for my intended usage, tight places and getting city scapes in. Works well up to about a seven story building size, if you know what I mean.
Mosfellskirkja Iceland, 24mm Sigma almost full frame, just a slight cropping of the flag pole which is ever present at virtually all of Iceland churches we came across. This would have been doable with a 28mm lens, but I would have been further back, therefore further down the steep hill. Fuji Neopan 400. This is a negative scan, the print I have is brilliant by comparison.
This was taken inside the Reykjavik Symphony Orchestra building, once again using 24mm. I was pretty much backed up against a railing to get this, anything longer and I would have missed out on this, or at least I would have had to be more selective than I already was. Sigma 24mm Fuji Neopan 400
This was a grab shot using 24mm in quite inclement weather. I had a parked car directly behind me, so I couldn't go back any further, I feel would have missed this with a 28mm as I pretty much know the pantograph would have been cropped out. Swinging the lens upwards would possibly have shown the wideness of the lens by allowing one to see edge distortion a bit more than by keeping the lens almost horizontal. Life is always a compromise, eh?. Sigma 24mm Fuji Neopan 400 and quite obviously taken around 1528 local time.
Mick.