Every winter, as temperatures dip, miles of tubing crisscross the ground in Woodstock, releasing a steady drip of water that freezes into icicles.

These icy formations sculpted into towering castles, illuminated by vibrant lights, drawing visitors from near and far will be open in early January.

As Brent Christensen, founder of Ice Castles prepares with his team to build these structures nationwide, he said while gradual climate warming is a concern, the more immediate challenge is sudden temperature swings.

“I think the concern is the unpredictability of weather or mid-season warm-ups,” said Christensen. “We’ll go from really, really cold to really, really warm that sometimes leads to us having to close down for a day in the middle of winter and it creates challenges for public relations.”

In some sections, the ice castles soar to 40 feet high, while other areas stand closer to 15 feet.

The pipes on the ground deliver water to specific spots where growth is carefully planned.

To fuel this growth, Christensen’s team uses “icicle farms” where ice is grown on racks, and by the next morning, the racks are laden with 5,000 to 10,000 freshly grown icicles.

These are transported to different parts of the castle, either laid at ground level to begin new formations or fused onto existing structures to build even higher.

Christensen’s journey into ice castles began in 2000, after moving from California to Utah.

With his family curious about the cold winters, he started experimenting. Instead of building typical snow forts one year, he set up a simple sprayer on a wooden structure, letting the water freeze.

Once he saw how the water froze into icicles, he started making elaborate ones with slides and tunnels without any structure underneath.

“I discovered that I could fuse icicles and formations and spray them, and they would grow in a really solid manner,” said Christensen. “That was my first start to making ice castles.”

The perfect weather for building and enjoying Ice Castles is crisp and cold — around 10 degrees at night and 25 degrees during the day. These temperatures keep the ice solid while staying comfortable for visitors.

But the structures can still hold up even if daytime temperatures climb a bit above freezing, into the low 30s.

Construction typically begins in early November, with the attraction opening by early January, depending on the weather. Once open, the castles let visitors through late February or early March, as long as conditions allow.

This year’s New Hampshire Ice Castles will have tunnels, caverns, towering formations, fountains, and icy slides. Guests can also enjoy unique features like horse-drawn wagon rides, a Polar Pub, a Mystic Forest Light Walk, and a whimsical Winter Fairy Village.

“It’s fun and we get to be really creative,” said Christensen. “We get to witness something really beautiful take shape and something that people really enjoy coming to see.”

Sruthi Gopalakrishnan can be reached at sgopalakrishnan@cmonitor.com