Inside a dormant volcano

Hikers in Iceland can enter the massive, empty magma chamber of the dormant volcano Thrihnukagigur, which rises 100 feet above Bláfjöll County Park and last erupted 4,000 years ago. 

From May 15 to Sept. 30, five tours a day are led by 3H Travel (phone +354 863 6640). On a 50-minute “moderately difficult” hike, the group walks two miles across hilly and uneven but mostly level lava fields; the last 10 minutes to the top of the volcano are the most challenging.

Small groups then ride an open elevator 390 feet down into the multicolored chamber, where they can stay up to an hour. The opening at the top of the cone is about 12-by-12 feet, and the ground space at the bottom of the chamber is the size of three basketball courts. Hikers can view passages that descend another 300 feet. 

The temperature inside is 37°F; hikers should wear warm clothing and hiking shoes and take water.

For the 5- to 6-hour tour, the cost of ISK37,000 (near $331) includes transport from/to hotels in Reykjavik (13 miles away), safety gear and a meal. 3H Travel also offers a helicopter to the peak, weather permitting, at ISK76,000 ($680) per person.