I often have this eerie feeling in Praga: I walk through some gate, or into some shop, or into a bar, and suddenly there is a whole new world opening in front of me. A world not quite matching the outside I have just left.
The same happens in ul. Kamionkowska. On the outside, there is a school and a street and cars and a normal, nothing-out-of-ordinary world. On the inside (try any of the gates on ul. Kamionkowska or the hole in the fence on ul. Rybna), there are uninhabited houses, huge piles of furniture lying around, stray cats and lots of interesting architectural details to be seen.
One more thing that might be interesting for you: ul. Rybna (Fish Street) was called that way because it used to be very near to a closed arm of the Vistula (hence Jeziorko Kamionkowskie which is actually a left-over from it). It is hard to believe now, but actually almost ul. Grochowska was the border of the riverbed.
Some of the houses in Rybna will be renovated soon, so it might be the last chance to see them in their current shape!