The pipe that is suppose to be connected to our shower drain is not connected and it is a straight pipe instead of an s-curve. Since we moved in a year ago it has had a horrible smell coming from it and when we plunge the toilet (which has to happen almost daily now compared to barely ever) it often comes back up from the drain in the shower. My husband looked down where the drain is and saw that the pipe was not connected at all to the drain.

We have been complaining about the smell since we moved in but the landlords answer has always been that the tenets before never complained (they were 4 college guys that were never home) so it must not be a problem. Now that she is raising our rent she is listening about the smell but treating to leave it until December because I said I needed it done before the end of August.

What can be going on under there? Is is safe for us to live with it like that?

[QOTE]what can be going on under there? Is is safe for us to live with it like that?[/QUOTE]
Your landlord has placed you in a unit that's a health hazard, ( in some states, if you take her to court you don't have to pay rent and may get back the rent you've already paid. Check with your local Building Department.)
Sounds like the shower isn't trapped and the unconnected drain produces moisture witch produces mold.( Which is also a health hazard.) With non trap you have a direct open connection to the city sewer that allows sewer gas to enter your home. This is a health hazard to you and your family and should be repaired ASOP. If the land lord drags her feet on this contact the Health Department and they will force her to repair or face a fine and a red g on the unit.
Don't let this go on!! Take action at once. Your families health depends on it. Good luck and let ne know how you make out. Tom