The Thor's Belt (also called Megingjord) is another artefact sought after by Lara in Tomb Raider Underworld.
In Mythology, the belt doubles Thor's already mighty strength, in the game it actually powers the two gauntlets.
Following her father's map, Lara travels to southern Mexico to find the Belt, there she discovers a secret passage to the Mayan underworld, Xibalba where the belt is carefully hidden and protected by the dead, or otherwise known as Thralls.
Like with the gauntlets, most of the artefact falls apart when Lara touches it, leaving only the original piece intact, which Lara places on her own belt buckle, immediately activating it and powering the gauntlets.
- The myth held that only with the additional strenght bestowed upon Thor by the enchanted belt, Megingjord, could he wield the weapon Mjolnir. Now I see that the belt - also ornately augmented by later users - is the source of power for the gauntlets. They channel the belt's power to those large special objects too large to move unless so equipped. Each of the two gauntlets I found must have contained a small amount of residual power in them that quickly drained without the belt to replenish them. I believe I have a good idea of how Thor's hammer might work when I find it. 
Reasons might be found on the "discussion page".
- Tomb Raider Underworld Journal Entry THOR'S BELT