Location from Undertale / Deltarune by Toby Fox
A maze-like facility at the Underground's heart — built by Gaster, powered by geothermal energy, and haunted by the ghost of its creator's ambition.
The CORE is the Underground's power source, built by W.D. Gaster before his disappearance. It converts geothermal energy from Hotland's lava into magical electricity that powers the entire Underground. It is also, possibly, where Gaster 'fell into his creation.' The facility is a dungeon in the classic sense — shifting corridors, encounters with the Underground's strongest non-boss monsters, and the path to Mettaton's final performance. It represents the technological peak of monster civilization and the mystery at its heart.
A gleaming, geometric facility of metal corridors and shifting layout sections. It feels alien compared to the rest of the Underground — more machine than architecture. Sections can rearrange. The path through is never the same twice.
Also known as: The Core