It's an indoor door, but it takes a key. It has a hole, but it's on the shaft between the knob and door. Simple probing doesn't seem to suggest any way to push or turn with a small screwdriver - but I didn't try with much effort since I didn't want to break anything.

Photos:

 

That hole won't do you any good without a key. It's designed to take the lock apart but in your keyless state, it won't help. Either call a locksmith to open and/or make you a new key, purchase locksmith's pick set, remove an external window to gain access or MAYBE, slipping a piece of very thin plastic back toward the latch through the crack to the right of the knob and that will only work if the lock doesn't have a deadbolt security plunger as part of the backset. If it has a security plunger and the lock was installed properly, the plastic through the crack won't work.

 

If you have access to the other side of the door, take the screws out and see if you can turn the latch with the knob off. I don't know for sure if that will work but it's something to try before hiring a locksmith.

 

Assuming you own the house and have permission to access the room if the above ideas don't work use a stiff putty knife to pry loose the stop strip starting at the bottom and working up. Cut the paint line with a utility knife. Once the stop strip has been remove you should be able to work it open with a putty knife.

 

Thanks Guys....

Putty knife and de-molding may be the way to go.

The door is from the walk in closet to an attic storage area.

Hinges on the other side. Molding around the accessible side blocking any card or putty knife entry. No windows, no access from above.

I'll have to figure something out soon, it's where I keep all the lego kits hidden from my son - and we're almost out of father/son group projects.

Might just call a locksmith and be done with it.

 

I suggest you get a different door knob too unless there really is a need to keep it locked as securely as it is. If not a good interior locking knob should be enough.