Define low level are we talking level 1-2 or 5-6ish? Do we have a typical party build of wizard/fighter/thief/cleric or smething different? Are we talking new players or experienced ones? Are their offlimits areas e.g. do you want to avoid "mature themes" or is it throw anything at them time? Why are they in jail in the first place? Are they not in jail but getting someone out? All these things can affect the way a game runs and what you want to include.
Some examples include . . .
1) A cleric could be facing heresy charges just getting out isn't enough if they don't gather proof of their innocence they'll be excomunicated from their order.
2) A mage could be constrained in the anti-magic area of the prison and if they destroy the orb that creates that rather than just getting her out then they releas other horrors that really should have been locked up.
3) If they are more experienced through other "innocents" in their way some of whom are genuinely innocent while others are just looking to get out to continue their crimes, smart ones don't take on the tough experienced adventurers but crop up later in a situation that makes it clear to the party they for example released a serial killer who's been targeting children ever since.
4) They stumble across a torture room perhaps with a victim still in it if the clerics not high enough level to heal him say he needs regeneration, heal or some other high level spell and they have to decide between putting him out of his misery, leaving him to suffer, or taking along someone who slows them down. You can make it quite clear his injuries will do that by limiting his movement/making him groan/bleed more if they try to carry him too fast.
5) If they aren't familiar with the prison lay out give them a time limit. You've escaped but the guards will notice you in X minutes and you have to be clear by then. There are the areas you were contained in low security cells, route to the entrance and you can retake that route if you remember it BUT that will take you through too many guards to slip round. If you take the alterate route you have to find an exit/exit plan before the guards notice and seal the prison.
6) Then you have the different areas a prisoner can wind up in. The low security area a series of progressively higher levels with group cells containing the prisoners, the high security area (extremely dangerous criminals who can present a challenge especially to poorly/lightly armed party members) which contain individual cells on a single level, the mage containment area which has anti-magic protections preventing them using their spells, the interogation/torture room, the guards break room, the showers/toilet area if allowed and they aren't required to go in their own cells, the armory containing the guards equipment + that taken off inmates, the oubliettes where the worst criminals are sealed in to die and be forgotten, possibly the non-humanoid containment area for creatures that aren't your basic elves/dwarves/men. All clearly marked perhaps but if you don't know the layout your looking at a lot of doubling back and forth in narrow corridors.