Two weeks ago on a day forecast to be uncomfortably hot and humid, accompanied by our grandson, Jack, age 12, we climbed into our car and drove north in search of relief.

Relief, in part, and also learning. One of our efforts as grandparents has been to treat our grandkids to some special experience each year as part of their birthday celebration. The treats have included forays to the Cities for Twins and Vikes and Timberwolves games, plays at the Guthrie and Children's Theatre and one at Central Lakes College, depending on age and interest.

In Jack’s case, we knew he was deeply (pun intended) into mining, having spent innumerable hours on the computer playing MineCraft as well as starting an excavation with a shovel on the family homestead outside of Pillager. What better than a visit to an underground

(as opposed to open-pit) mine?

A few minutes of research on the computer revealed exciting information. North of Duluth, on the south shore of Lake Vermilion, in the Soudan Underground Mine State Park, is Minnesota’s oldest, deepest and richest iron mine, now designated a National Historic Landmark.

The surface buildings of the mine are open to the public, and during summer months there are daily tours of the mine. Visitors are lowered in an 80-year-old electric mine hoist to level 27, the mine’s lowest level at 2,341 feet below ground.

As might be expected, the temperature down there stays in the low 50s, day and night, all year long. No worries about heat, humidity or, for that matter, rain. A visit here would not be affected by the weather.

We called Jack, set a date, called the park and ordered tickets. Cost for two adults and one 12-year-old was $46. Our tour would start at 1 p.m. and end at 2:30 p.m. We were told to arrive at least 30 minutes ahead of time and warned to wear warm clothes and sturdy shoes.

When we arrived at the park we explored the surface buildings and learned about the history of the mine. In the late 19th century, prospectors searching for gold in northern Minnesota discovered extremely rich veins of hematite at this site, often containing more than 65% iron. An open-pit mine began operation in 1882, and for reasons of safety switched to underground mining by 1900.

From 1901 until the end of active mining in 1962, the Soudan Mine was owned by the United States Steel Corporation. When the mine closed, the underground workings consisted of more than 50 miles of lateral tunnels, called drifts, and vertical shafts, or raises. The primary underground mining method used was known as cut and fill.

This involved mining the ceiling and using Ely Greenstone and other waste rock to artificially raise the floor at the same rate as the ceiling was being mined out. As a result, the floor and ceiling were always 10-20 feet apart, and waste rock never had to be hauled to the surface, since it was recycled.

From the moment we put on the mandatory hard hats and stepped into the steel cage that lowered us a half mile into the cooling confines of Mother Earth, through the jostling ride in open-air train cars some three-quarters of a mile back and forth in the shadowy confines of the level 27 drift, until some 90 minutes later when we rose back to the surface, non-stop learning occurred for all of us.

The guides were engaging, the experience of being underground struck us as both spooky and exciting, and the fun of doing something new was just plain satisfying.