Trolls are rebuilding your abandoned kingdom beneath the mountain in In the Hall of the Mountain King. With muscle and magic, you will unearth riches, discover collapsed tunnels, and dig out great halls as you raise the toppled statues of your ancestors to their places of honor at the center of the mountain. Gameplay is driven by the novel cascading production system. Timing and tactics are essential as players work to restore your home to its former glory and win the crown!

Working on the same board game with the other players (but starting at your own entrance), you will dig a competing network of tunnels by spending more and more valuable materials to place tiles onto the map. You want to lengthen your tunnels to connect with buried gold and materials, with workshop locations that can alter resources, and especially with toppled statues. Statues are essential to scoring, and you will spend to move them through the tunnels to best scoring locations near the center of the mountain.

A major part of the game is the cascading production. You start with a line of 4 trolls, and every troll shows the combination of resources — gold, stone, iron, marble, carts, runes, and hammers — that it creates. When a new troll is hired, place it above two other trolls, forming a "pyramid". The new troll starts, obtaining its resources, and any trolls underneath it ALSO activates, obtaining any resources that they have room to carry. In this way as you hire more trolls, you obtain greater windfalls of resources as the end of the game comes closer. The schedule of your hiring turns against your building turns is important as you attempt to maximize your cascades while making sure you get the trolls you want from the shared market and also stay competitive on the map.

The game ends soon after the last player hires their sixth troll, then the player with the most honor (earned for digging tunnels of increasing quality, for excavating great halls, and for arranging statues closer to the heart of the mountain, especially onto matching pedestals) is crowned the Mountain King and wins!