The 50th St. subway station in Manhattan on the C line holds a secret. Peak through the crack between doors at the end of the platform, and you can see an old turnstile and staircase leading to the street.

It's one of 111 stations where the MTA has shuttered at least one staircase or entrance. Many were sealed in the 1970s and '80s, to make stations safer as crime soared in the city.

"It's just sitting here, rotting away, abandoned," Brian Lee, an engineering student, said.

Lee is one of several advocates in a group called ACCESS, short for Accessing Currently Closed Entrances to Subway Stations. It has compiled a list of every shuttered entrance in the system, and hopes to build community support for reopening some of them.

"We found that roughly over a million people live or work closer to a closed access point than an open one," Alan Minor, a co-founder of ACCESS, said. "So that has impacts on, not only commute times, but economic opportunity."

A wall at the end of a platform at the 103rd Street station, near Central Park, on the B and C lines hides a former entrance. City Councilman Mark Levine has been trying to get the entrance open.

"There is one narrow stairway in and one narrow stairway out for the entire station on the uptown and downtown side," Levine said. "Simply from a safety perspective, it's scary."

A Brooklyn community board wants the MTA to reopen entrances near Nostrand Avenue on the A and C lines, saying the neighborhood is in the middle of a development boom.

Commuters wouldn't have to walk an extra five minutes to Nostrand Avenue just to catch an express train, if there was a station entrance at Bedford Avenue, where one stood decades ago.

"You can't have two to three thousand people living on the corner and sending all those people to one entrance at Nostrand Avenue," said Henry Butler, district manager at Brooklyn's Community Board 3.

One concern at the MTA is that reopening a closed entrance could trigger a federal requirement to add a costly elevator if the station does not already have one. The MTA says it will review requests on a case by case basis.

Editor's Note: A previous version of this article misidentified a station entrance on the L line at Avenue A and 14th Street as being "reopened." It is a new entrance.