The most charming train line in the mostly uncharming New York City Transit system is Brooklyn’s Brighton Line, between Prospect Park and Coney Island.

The line carries the B and Q trains on the right-of-way of the Brooklyn, Flatbush & Coney Island Railroad, a surface steam railroad that began operation in 1878, connecting Prospect Park to the Hotel Brighton on the Brighton Beach waterfront near Coney Island Avenue. In 1887, it got a new name: the Brooklyn & Brighton Beach Railroad.

In its early years, the line ran through farms and fields. Having already been extended to Atlantic and Franklin avenues to interchange with the Long Island Railroad, the line entered into a contract in 1896 to run its trains from Franklin Avenue along the Kings County Elevated Railway Company’s Fulton Street tracks to downtown Brooklyn. The Brighton Line was then fully electrified, and in 1900 the Kings County El took full control of the Brooklyn & Brighton Beach, which that year crossed the Brooklyn Bridge into Manhattan.

In other words, in 22 years a seasonal resort railroad that traversed the countryside became an integral part of the regional commuter rail network as subdivision after subdivision swept away the farms of Flatbush, and then the racetracks and resorts of Gravesend.

Later in 1900, the Brooklyn Rapid Transit (BRT) Company absorbed the Kings County Elevated, and between 1905 and 1908 rebuilt the Brighton Line.

Two things bring charm to the line. One is that many of the original subdivisions of early 20th-century Flatbush remain intact. These planned communities are picture-perfect railroad suburbs of riotously eclectic bungalows and mansions on tree-shaded streets, many with brilliant design flourishes such as landscaped medians, or the illusion of spaciousness that comes from planting trees at the house line rather than the curbline. It’s fair to say that for cleverness of planning and quality of architecture, these communities rank among the finest of their kind in America.

This would not be evident to riders but for the other thing that makes the line so delicious: From Prospect Park to Coney Island, the trains run entirely out of doors. From Prospect Park to Avenue H, the trains run in an open cut. From Avenue H to Sheepshead Bay, the trains run on an embankment. From Sheepshead Bay to Coney Island, the trains are elevated. The stations have the air of country railroad depots.

The way to savor the Brighton Line is to get an unlimited-ride MetroCard. You can then get off at a station, walk around the neighborhood until your 18 minutes (which must pass before you can use the card again) are up, then carry on. Here are a few recommendations, amounting to my idea of a perfect day in New York City.

Get off at Church Avenue. You’re at East 18th Street, in the heart of Flatbush, a neighborhood with a dual character. When you get off the train, you’re in an intensely urban neighborhood, a largely Caribbean community teeming with street life, with reggae forming an omnipresent background music and stores spilling cornucopias of island produce onto the sidewalks. But two blocks to the west you can turn left onto Buckingham Road into the fairy-tale land of Prospect Park South, the most magnificent of all the planned developments of “Victorian Flatbush,” with one improbable mansion after another.

From here the trains run south on a line between East 15th and East 16th streets. Get off next at Cortelyou Road. You’re in the increasingly popular Ditmas Park neighborhood. Cortelyou Road is taking shape as a lovely village-like main street. You’ll have enough MetroCard time to walk to East 19th and take a right. Walk one block to Dorchester Road, where begins a planned community similar to, though homier than, Prospect Park South. Look for 463 E. 19th St., at the end of the block at Ditmas Avenue. The 1906 Colonial Revival beauty was designed by the great Brooklyn architects Slee & Bryson and has a rounded, jutting front porch with the most beautifully turned wooden balusters you’ll ever see.

Next, stop off at Avenue H. The unusual station house dates from 1906 and was built as the sales office of Thomas Ackerson, the developer of Fiske Terrace, yet another beautiful planned community, recently named a historic district (a status Prospect Park South and Ditmas Park had already attained). Ackerson sold the development’s last house just as the BRT was building the new Avenue H station, and the transit company decided to incorporate Ackerson’s very rural-looking wooden sales office into the station complex. It is the only station house in the transit system built for another purpose. Walk to East 17th Street and take a left. Here are the landscaped medians called the Midwood Malls, created by Ackerson, lined on both sides by the lovely houses of the Fiske Terrace-Midwood Park Historic District.

It will be enough for one day to go just one more stop to Avenue J. This way you can experience riding on an embankment. And you can stand in line — every minute is worth it — at Di Fara, right by the station at 1424 Avenue J. Not until I ate one of Domenico DeMarco’s pizzas, considered by many to be the finest in the country, did I understand the Baroque.

fmorrone@nysun.com