If you’re in Grand Central at 11:30 a.m. Monday, and you spot what looks like a really -- really -- old train on the uptown 4 and 5 express track, you’re not seeing things.

It’s the MTA’s low-voltage “Nostalgia Special,” which the agency rolls out now and then for special occasions like, say, Opening Day at Yankee Stadium.

The train will ride on the 4 line to the stadium, departing around 11:30 a.m. for the 30-minute trip. The cars are 1917 Lo-Vs that once ran on the IRT line.

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They were retired 50 years ago when the fare was 15 cents.

No nostalgia on that -- you still have to pay $2.75.

Hopefully, the only nostalgia Monday will be those old subway cars -- and not the Bombers losing ways last season.

The Yanks are playing the Toronto Blue Jays at 1 p.m.

Play ball!