Pissed About Piss

Ever since we moved into our apartment about once a month the entry way starts to give off a terrible odor. Until now it's been unclear what it is. It seems to show up when there are a lot of plants and construction equipment in the entryway. However, recently the smell has gotten much worse. Having grown up with three fussy cats who liked to urinate in places they weren't supposed to I am convinced that the situation must be one of the following three things:

a) The plumbing for the bar bathrooms (we live above a bar) on the first floor has gone bad and is leaking urine into the foundation of our apartment building.

b) Someone is sneaking in (or maybe they are residents, but our neighbors don't seem the type) and peeing all over the floor of the entry way.

c) Someone is sneaking in and letting their overly hydrated cat piss wherever it pleases and it chooses the entry way.

Thank G - D the smell doesn't reach the third floor. Hopefully it will be gone by tomorrow morning.