Eight miles from downtown Boston, I stop in my tracks before a water-stained, dilapidated wall cowering below the growth of a thick full forest. In a corner of the wall, I spot an eerie opening fixed open by a rusted-shut doorway. Alone, I look in and see tunnels splitting into three directions, one leading into some sort of inner courtyard. It feels ancient. I wait a second, then go in, scurrying straight through, not glancing at darker passageways leading left and right, and enter the courtyard. Almost wincing, I look up to find… a picnic area.

This is Boston?

This is a battery at Peddocks Islands’ Fort Andrews, opened at the outbreak of the Spanish-American War in 1898. And it’s one of the more adventurous ways to spend a day in the Boston Harbor Islands, called the “fair emeralds on a sapphire plain” in the 1882 King’s Handbook of Boston Harbor by MF Sweetser. Most of the 110,000 who visited via ferry last year just go for sea, sand, and forts. Others to camp.

Ferries go to six of 34 islands, but two stand out for visitors. Hilly Spectacle, one of the closest to downtown, is rimmed with beaches and holds clambakes, yoga, and jazz concerts. The other, the main ferry hub of Georges, is home to a spectacular star-shaped fort that nearly fills the island. Built in the mid 1800s, it’s fame came as a Confederate POW prison during the Civil War. Near rebel VP Alexander Stephens’ cell, an unsigned stairwell leads up to grassy ramparts and observatories for 360-degree views.

I’m pleasantly impressed with Fort Warren, but want to see one of the lesser-visited islands too. Grape Island is known for its woodsy trails; Lovells for its swimming beaches, old batteries, and campsites; and Bumpkin has a great name. But I pick Peddocks, where only three-percent of visitors go. Slender, and 1.5 miles long, it’s one of the harbor’s biggest, with tall buffs on either end, and rocky shoreline good for swimming nearly the full way around.

Three bearded Bostonians in their late 20s drink Bud Lites and join me on the 15-minute ride from Georges to Peddocks. “This is my bachelor’s party,” one explained, when I ask what they’re up to. “I had no idea what was out here.” As a send-off, his brother arranged a stay in one of the six $40 yurts that opened on the islands last year.

The pier leads into the Fort Andrews site, with 14 old buildings. Behind the barracks, a trail winds to six yurts. I wander past old red-brick barracks and officers’ quarters (all closed off to visitors), then find my way to the overgrown battery.

This is weird and fascinating, but I’m keen to explore the other end of the island, where there’s a community of a few dozen cottages that are remnants of Crab Alley, a Portuguese fishing village established over a century go.

View Images A buoy-covered cottage sits on one of Boston Harbor’s largest islands, Peddocks Island (Photograph by Robert Reid)

I walk along a three-quarter mile stone beach towards a bright pink cottage I see way ahead. Behind it I find a row of simple wood cottages. A couple condemned ones covered in buoys lean like drunks on sidewalks, others are brightly painted with armchairs next to well-kept gardens.

Outside one, I meet Kurt, an “islander” who wears old turquoise shirts and a silver dolphin necklace on deeply bronzed skin. He’s been coming all his life.

“This is the best thing I ever did,” he says motioning to his white cottage as classic rock music plays on a battery-powered radio (the cottages here have no water or electricity). “I bought this cottage for $700 in 1981.” Kurt also lives on the “mainland” south of Boston, but is out here much of the year. “Ten degrees is my line. Below that, and it’s too cold.”

He says every now and then the city tries to clear them out, bringing the matter to courts in 1970 and 1991. No one’s moving. As one local here once told the New York Times, “Our feet are tied to the ground.”

“We’re islanders,” Kurt explains simply. “And we have nothing like this in Boston.”

Glad I found it.

To do this trip:

The Boston Harbor Islands Ferry leave Boston from North Long Wharf. A day ticket is $15. A new visitor center, a block in from the water, has a ranger with information on island activities.