The heat is on in the city, especially in the subway. 

As hot as it has been above ground, it has been much, much worse below.

"It's as hot as it could be be," said one commuter.

"Can't wear shorts to work, can I?" said another.

Ok, it's hot. But just how hot is it? 

The Regional Plan Association took the temperature of the 10 busiest stations Thursday. The average reading: 94.5.

But we wanted to know: What are the sweatiest stations in the city? On Thursday, we set out with a hand-held thermometer to find them.

At Queens Plaza, it was a very temperate 85 degrees.

At 34th Street and Penn Station on the 1, 2, 3, we got warmer. The thermemoter clocked in at 93.5.

"Pretty hot, pretty hot!" said one person at Penn Station.

"It's hot. It's hotter than the outside," said another.

But not as hot as beneath 14th Street and 7th Avenue. Our reading: 95 degrees.  

"It feels like Washington DC in the summertime. Its just swampy," said one commuter at that station. "It's really, really hot. It's gross. I no longer wear work clothes to work."

Still, we knew we could find even worse. Some real triple-digit misery. In Lower Manhattan, we were right. It was 105 degrees at Brooklyn Bridge.

Subway experts say the hottest stations tend to be the underground terminals. And Brooklyn Bridge is a turnaround point for the 6 train.

As at other terminals, trains often park there for long periods, belching hot air-conditioning exhaust onto the platforms. 

"The stations are old. They need to be rehabbed. They need better ventilation," said Moses Gates of the Regional Plan Association. "The trains are heavy. They stop and start, which throws off a lot of heat."

It was also 105 at the L train's last stop at 14th Street and 8th Avenue.

Hot, yes - but we thought we could find even worse. At another terminal, the end of the E line beneath the World Trade Center, we were right. It was a Death Valley-like 106.5 degrees.  

"It feels hotter, because it's wet and humid and stuffy and the air doesn't move around at all," said one commuter at that station. "Sweltering. Absolutely sweltering."

But there are spots throughout the transit system that may seem like a relative oasis from all this heat, like the platform at the 34th Street-Hudson Yards station, where the temperature on the platform was a relatively chilly 78 degrees.

Also refreshing: beneath the cooling units on the Lexington Avenue Line at Grand Central, it was a cool 78.5 degrees. An island of chill in a sauna-like system.