My yard is barely visible from the sidewalk, thanks to a snaggle of untamed evergreens atop a four-foot-high retaining wall. But behind that ragged urban barrier, the property opens out onto a surprising double-lot expanse of serpentine flowerbeds, an oasis of hammocks and bluestone patios, cedar pergolas and grassy terraces. An oversized cast-iron smoker hugs the fence line (on standby for twice yearly pig roasts), and the parking pad in front of the garage has been known to serve as a temporary abattoir, which is a nice word for describing what happens when my husband takes a Sawzall to the deer he gets from bow hunter culls of nearby parks.

I married into the home-based butchering, but the rest of this secret garden is all me. I trash-picked the trellises. I found the zero-gravity chairs on sale. I planted the carloads of perennials, I laid the schist walls, and I positioned the rubber snakes and lizards onto rocks so that visiting children could spy them with their little eyes. I built the cloistered garden - my first ever - from scratch, and 16 years later, my efforts have led to a retreat from the very city that houses it.

Mine is not the only facade in town that hides a private paradise. In East Mount Airy, labor mediator Alan Symonette brought his childhood love for model trains out into the light about five years ago, after taking a course in garden railroading at Morris Arboretum. Symonette already owned three types of trains (Lionel, HO, and N), but established his outdoor railway with a new set of G-gauge trains, which are larger and run on rustproof brass tracks.

"I've always gardened to a certain extent," Symonette explained, "but this is another dimension."

He has created orchards out of small-leafed basil plants, turned prefab wooden birdhouses into buildings, and constructed a tunnel using cinderblock and wood, with ivy and ferns planted on top. Symonette runs the trains only from May until Halloween, but says the maintenance is a four-season proposition. Hurricane Sandy wreaked havoc on his locomotive barn, for example, so that's a repair for the spring. In winter, his biggest challenge is stray cats who mistake the tunnel for a home.

In Narberth, 7-year-old Derek Bierschwale is training for his life's dream, which is to appear on NBC's American Ninja Warrior. He has 14 years before he can actually apply, but to get him started, his father, architect Ralph Bierschwale, constructed a mini-version of the TV show's obstacle course alongside the family's driveway. Debby, Derek's mom, says that their course currently features junior versions of the show's "cliffhanger" and "unstable bridge" segments, and that next spring, her husband will add on a "lamp grasper" and "salmon ladder." Whatever those are.

Within a four-block radius of my home, I've discovered other hidden worlds. There's a couple (she's a dancer and he's a puppeteer) who turned their garage into a theater, complete with spotlights, a stage, and salvaged auditorium seating. Another pair (world traveling aesthetes, musicians, and gourmet cooks) took the roof off their garage, installed a 700-degree pizza oven in one corner, a table in the middle, and a candelabra above, creating the most elegant al fresco dining room I've ever seen.

Two doors down from me, my friend Claudia Raab has filled her garden with dahlias. Claudia - whose limitless exuberance is not generally hindered by obsession to detail (she has lost her wallet only to find it in the refrigerator, and she claims that the amount of crumbs spilled onto the floor of her car would have kept the Donner party from turning on itself) - minds her dahlias with meticulous attention.

Claudia started with several dozen bulbs a few years ago, flowers that bloomed coral and fuschia and a near-black purple, in tightly lobed little clusters and then as big as dinner plates. Claudia loved them not only for the bouquets they made, but because they'll come back each year - if cared for correctly. Each spring, she rigs up Goldbergian cages and trellises throughout her yard, watches the plants grow without fuss through the summer and then bloom riotously for three months straight, well after most plants have called it quits. For this she's willing to dig them out at the end of each season, carefully hose them down and trim off stems (to reduce rot), and then, once they've dried, appear at my door with slatted crates full of her darlings, ready to winter them in our heated garage.

"It's fun to grow a million different kinds," she says, "and I love that they're sustainable. You don't have to keep buying endless amounts of them, and eventually, they start to multiply." This also works out well, budgetwise, since dahlias can easily cost $10 per bulb.

I see what other people do in the privacy of their own gardens and I try to imagine what earthborn dream I might tackle next. Koi pond? Corn field? Open-air movie theater? The neighbors I directly abut would probably have no objections to any of my fantasies, except the one I hold most dear: miniature donkeys. Sadly, they are probably better suited to a back 40 than a backyard.