What is inside anthills?

This 27 December 2019 video says about itself:

When you look at a fire ant hill — or mound as it’s properly called — you’re actually seeing just the top of an enormous underground structure: the ants‘ nest. Inside, a vast network of tunnels and chambers plunge up to 2 meters into the soil. Ants ferry their young up and down these tunnels to keep them at the best temperature to grow.