Riddled!

After crossing the mountains and sea, the Guardians found themselves reunited on a wind-blown desert. The desert seems to stretch on away from the mountains and sea forever. The only noticeable feature on the entire barren landscape was a small iron tower, approximately 30 feet tall.

The tower was completely deserted and entered through an unlocked portal on the ground floor. Inside was a single case of stairs that spiraled up to a small room on the top floor. The room itself was completely empty, save for the spread jawbones of what appeared to have belonged to a huge shark, which hung upon one wall. Between the Shark's jaws lied the shimmering portal to the second Circle of Hell.

Written in blood above the jawbones was the following message: "He would descend into the next realm must first answer a query; 'Kneeling 'fore heat, coursing through vein; air is its foe, water its bane. At times this a steal, but not a crime. Is your wit as sharp as this rhyme?"

Eventually the word "Iron" was spoken aloud, and the Guardians were permitted entrance to the second level of hell.