How much damage do you want to make to the door.
It's hard to guess without seeing it, if the lock strip has fly out straight bolts and the hinges are exposed you can slice through pins with angle grinder.
If the lock unlocked but the handle won't move, remove handle and spray where ever you can with wd40, into the internals of the lock, leave for a bit and wiggle lock back and forward and tap with hammer at same time.
If lock barrel has gone it usually only fails from one side, can you feel any weight on the mechanism while it's turning, sometimes locking and unlocking a few times with oil added will help free a stuck spring.
If a spring has snapped or something on the lock strip has come apart or is stuck solid it can be a pain.
If it's got glass and or a panel and the lock strip is not hook bolts or locking rollers you can remove the glass and or panels and it gives a lot to play with to try and prise the door open.
If it's the lock barrel drill it out, drill it just below the key way till your through all the spring tumblers, hoover out and use screwdriver in lock.
All else fails, recip saw and a new door
One of my last jobs before crimbo was lost keys on a security lock and no access to the inside of the property