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The winding caves that tunnel under the city of St. Paul tempt many a would-be explorer. But city officials have one urgent message: Don't even think about it.

After three first-responder dispatches to the caves in the last month and a half alone, the city's Fire Department is once again asking people to stay away from them. It is illegal to enter them, and the Fire Department has sealed off many of the entrances with blocks of concrete or fences for safety purposes, said St. Paul Fire Department spokesman Roy Mokosso.

"When [people] do these sorts of things, they risk injury, and they also risk injury to potential folks that will probably be dispatched to respond to their emergency," Mokosso said.

More than 30 teenagers were escorted out of a cave in Crosby Farm Regional Park on Friday after a member of the group worried that their friends were in the cave too long and called 911, Mokosso said. No one was injured, but 28 firefighters responded, he said. The Fire Department was also dispatched a few hours later to S. Mississippi River Boulevard to undergo a technical rescue.

The caves are dangerous, Mokosso said, because of poor ventilation and carbon monoxide gas, in addition to poor visibility and uneven terrain.

Although the department has tried to barricade all cave entrances, the soft sandstone surrounding them is easy to penetrate, said deputy chief Steve Sampson.

"Unfortunately, the will of some of these urban explorers surpasses the ability to essentially prevent them from coming in," Sampson said. Rainstorms and weather can also create new, hard-to-find cave entries, he said.

The Fire Department is dispatched to the caves four to five times a year, Mokosso said. There is no cellphone service in the caves, which makes it impossible to call for help within them.

Some of the St. Paul caves open up into large spaces where groups of people like to hang out or have parties, which is what the 30 teenagers were doing before the Fire Department was called Friday, Mokosso said.

With the proper equipment and experience, cave exploration can be an exciting "quest into the unknown," said Martin Larsen, president of the Minnesota Caving Club. The group has explored dozens of miles of caves— with property owners' permission— and mapped out newly discovered terrain. "If people are interested in caving, do it the right way," Larsen said.

Having to reseal caves after people break into them drains city resources that could go to more important things, Sampson said.

"I get it's an enticing trap … to go and explore," he said. "But if they had full knowledge of ... the dangers and hazards that are down there, as well as some of the [incidents] that we've had that have included the loss of life or injury, I don't think they'd be so apt to go in there."

Michelle Griffith (michelle.griffith@startribune.com) is a University of Minnesota student on assignment for the Star Tribune.