OLIVE HILL, Ky. -- It was a beautiful day in the neighborhood -- at least underground.

With an icy, slippery morning giving way to incessant rain, cold and slush, it was the perfect day to just go underground and stay for a little while.

And, oh, the places you could go when you got down inside.

More than 600 cavers from all over the United States and Canada descended upon Carter Caves State Resort Park on Saturday to try out a couple of the dozens of different trips available during the first full day of the 24th annual Crawlathon, which started Friday and wraps up today.

Saturday morning, Lisa Plummer, wife of park naturalist Sam Plummer, said 560 had pre-registered for the weekend’s 89 different trips.

Quite a few more cavers registered on Friday to get in last-minute on the weekend, which offers a once-a-year backstage pass of sorts to some of the prime-time caves on public and private property in Carter County, which is pocked with more than 200 caves.

Headquartered at Carter Caves State Resort Park, which holds 20 caves with six open to the public, the Crawlathon was started by former park naturalist John Tierney and current park naturalist Sam Plummer.

Park staff are assisted by a small volunteer army of area cavers, many from the Flatwoods, Ky.-based Eastern States Speleological Organization, founded in 1968 at Marshall University.

Partnering with the host ESSO Grotto are nearly a dozen other caving groups from the region that support the weekend.

Kathy Largen and her husband, Charles, came up from Virginia. Cave guide Rick Nelson came back from California, and Jason Griffey, 31, of Suwanee, Tenn., came back to the park where he worked five summers to guide trips including the "Bat Cave Back Door," which gave a good 30 hard-hat wearing explorers 2 ¹/₂ hours of all the wet, 12-inch-high spaces and narrow passages they wanted.

It didn’t take long for Griffey, who has spent an estimated 400 hours in Bat Cave giving tours, to get his guide voice back.

"We’ve got 24," Griffey said counting heads at the start of the trip. "Hopefully, we’ll make it out with at least 22."

For many, Crawlathon offers a safe chance to taste adventure, whether it is three hours of crawling and wiggling through tight cave tunnels or heading over the side of the hill on a rope.

Custom-crafted for ages 6 and up, scout troops and cavers of all levels, Crawlathon includes such day trips as "Caving for Kids, "Extreme Burchett," "Caving 9 to 5," "Ascension for Idiots," and "Sandy Cave Flotilla," in which cavers lower a small boat down through a small, gumdrop-shaped hole and ride it through the water to a sandy shore where they tromp throughout the large halls and some narrow holes in Sandy Cave, which is part of the Cascade system.

The lure of exploring the netherworld brought Justin Burr, 24, on a serious weekend road trip.

Burr said it was a great chance to try some different caving after he got turned onto the sport while working on an archaeological project in Belize this past summer.

Merlin Tuttle, the founder and president of Bat Conservation International, spoke Saturday night, and Saturday morning, cavers tried their crawling skills in the new and improved Squeezebox, which was cranked down as low as six inches for smaller kids to slide through.

Pittsburgh resident Zarrin Leff, 19, slipped through the 7-inch-high space in 55 seconds with his dad, Scott, 50, cheering.

For the two, Crawlathon has been a fun wintertime family tradition for the past 11 years.

"There’s always a lot of cool trips, and they just keep coming up with new ones," said Zarrin, who went on the Carter City Connection, a new trip on private property, with his dad on Saturday. "It’s really become a father/son tradition."