All depends what you're hidey hole is intended to do and what are the considerations go in. My biggest are preventing kids from getting to a gun outside my safe. Second is the hidey hole must serve the purpose of availing a gun where an attacker might ordinarily think I'm vulnerable. And also keeping it in a place the average occupant in my house wouldn't find it.
Saying that I have two hidey holes. One in my walk-in closet that locks from the inside(meaning I lock it with a key from the outside). When I had to redo the walk-in(my Dad owns the house, we kicked out the tenants so I now technically 'lease-to-own' for various fiscal reasons) closet I had to redo the walls, ripping most of the drywall out. When I was redoing it I thougt, hey the space from the door jam to the inside would be wider and thicker and I could put some crown molding up in a strange fashion to make it look I'm reinforcing the door frame in an odd fashion. I put on side, an inside hinge that can't be seen by the naked eye and I put a fabricated latch of sorts at the very bottom of the floor. You'd have to know what you are looking to press the release latch cut into the crown molding and then the crown molding turns away from the extra space of the wall width. An there you have a pistol grip shotgun and couple boxes of extra shells. I had the extra time and spare crown molding for free, the hinge didn't really cost anything and making the release latch of sorts only took a couple of hours. I haven't showed it to anybody, and people ask when they see my safes in my walk in closet and never ask about the crown molding.
The idea being that should someone break into the house while I'm just getting home and don't have a gun on me for any reason(coming home from lawshcool where we aren't allowed to even have guns stored in our cars). I can run to my room, knock the door to my room off the frame easily enough(I intentionally put on a light door for said reason, I have renters insurance on my stuff and all my guns and ammo are locked up in my safes in a locked walkin closet). The trouble will be unlocking the closet. Then I'd just shut the closet buying me the necessary second or two to undo the latch, pop out the shotgun with one hot in the pipe and the safety off.
The second one is for a spare Taurus PT 92 I have, mind you I have the master bedroom. I had to redo the lighting in the bathroom(one shower and one toilet) so I put in track lighting because it is easy enough I noticed that if I stood on top of the rim of the toilet and put one foot on the counter where the sink is I could reach up inside what I called the lighting cavity. The track lighting took up far less space than the original flourescents(the long bar ones). So I cut out a piece of the drywall inside the lighting cavity and the roof cavity was right on the other side(mind I'm not technical term astute). I created a cubby out of scrap pieces of would that I nailed together that'd fit inside the space and put back the original cut piece of drywall. So kids can't easily get to the gun unless they are at least 5'9" because I just barely reach it and it's well hidden. You have to look real close to see the lines and have to be looking directly at it. I've had my roomate and several others look at the track lighting and not seen the cuts which I did in a series of cuts.
To get the gun I just push one side of the cut piece and it turns in and I can pull the piece right out to get to the gun. So if I get up in the middle of the night and don't bring a gun with me(which is funny given that I keep the gun in the bathroom because if someone breaks in I'm locking myself inside the bathroom where my cell phone charges during the night), and I hear one of my windows break or my door I can sand up on the rim of the toilet (without the seat) put one foot on the counter and get to the gun. Mind you I shoot the pistol at least once a month and I cycle out the ammo.
So there's my little bits of paranoia for you lol. It's cheaper than a shrink.