Short answer: many park benches are fairly easy to disassemble, but it really depends on how the bench is built. Most residential and commercial park benches use a bolt-together frame with separate legs, seat slats, armrests, and a backrest. If that is the style you have, you can usually break it down enough to get through a narrow doorway without too much trouble. If the frame is welded or cast as one piece, your options may be limited to removing the wood or recycled plastic slats and some hardware, which only reduces the size slightly.
From my experience, the easiest park benches to move are the ones that arrived as knock-down or partially assembled kits. These models typically use hex-head bolts or Allen screws at the main connection points: where the legs meet the seat support, where the armrests attach, and where the backrest connects. With a socket wrench, a set of Allen keys, and a standard screwdriver, you can remove those connections in about 20 to 40 minutes. I always recommend taking photos before you start and placing the bolts, washers, and nuts into labeled zip bags. That simple step makes reassembly much less frustrating later.
If your main goal is just to fit the bench through a narrow doorway, you usually do not need to strip it down completely. Start by removing the legs, then test the width of the remaining seat and backrest assembly. Most interior doorways are roughly 30 to 36 inches wide, and a bench with the legs removed will often slide through on its side. If the opening is tighter, removing the backrest and armrests can reduce the profile even more. Wrap the large pieces in moving blankets or furniture pads to protect the bench and the door frame from scratches.
There are some cases where park bench disassembly is not easy. Older benches and heavy-duty commercial models sometimes have rusted or painted-over bolts that need penetrating oil and extra leverage to loosen. Fully welded steel frames and cast aluminum end frames may have very few removable joints. In those situations, you may have to angle and tilt the bench rather than take it apart, but that can be risky in a very narrow hallway. If you are dealing with an opening under 28 inches, you may also need to remove the door stop, hinge pins, or even the door itself to gain a little extra clearance.
Before you buy or move one, check the product manual or listing for terms like "assembly required," "knock-down design," or "bolt-together frame." Those are good signs that you will be able to disassemble the bench for tight spaces. If the listing says "fully welded" or "one-piece frame," plan on moving it whole or through a wider entrance. Overall, if your park bench has visible bolts and separate legs, the answer is usually yes: it is easy enough to disassemble for moving through narrow doorways as long as you have basic tools, some patience, and maybe a second set of hands for the heavier parts.