Monument of Ruin

Monument of Ruin also known as Fake Nazarick is a fortress located in the center of the Great Forest of Tob.

Background
Ainz Ooal Gown, wary of the New World and its potential dangers, commissioned its creation. Aura Bella Fiora was the major architect of the structure; it was to provide a hiding place in case there was an emergency and he could not return to the Great Tomb of Nazarick. In addition, it would act as an alternate base of operations to avoid Nazarick's location being revealed.

The Dark Hero Arc
Ainz commissioned Aura to create a edifice that would serve as a shelter in case any denizen from Nazarick was attacked by an unknown force.

The Show Must Go On!
Aura started work in creating the secondary base with the help of several Dragonkins. Mare had tagged along and was confused at the purpose of the structure. And when Aura declared that she was building a second Great Tomb of Nazarick, Mare became concerned as he feared it meant that she was seceding from Nazarick. However, Ainz arrived and explained that the base would serve as a base to lure potential enemies in case anyone from Nazarick was attacked.

The Sealed Evil Tree Arc
Aura reported to Ainz that everything was going smoothly with the constructions when she met with him and Hamsuke. Later after meeting the dryad, Pinison Pol Perlia and learning of the existence of Zy'tl Q'ae, Ainz wished to observe it, worried it might be a threat to his new base in the forest.

The Lizard Man Heroes Arc
Aura is seen directing several elder liches, golems and imps. When her watch declares it is time to be lunch, she orders them to take a break. Eventually, she managed to finish building the structure, in time for Cocytus to use it as a base of operations to direct his army of undead against the Lizardmen Alliance.

Later after Cocytus failed in his mission, Ainz and the Floor Guardians used it to safely watch the fight between the warriors of the lizardmen and Cocytus.

The Two Leaders Arc
The construction of the fortress was noticed by several native inhabitants in the Great Forest of Tob. Those that approached the structure, were killed. The Gigu Tribe for instance, learned of its existence when several of their surviving warriors brought news of it to them. From them, they learned that a new power had suddenly emerge out of nowhere and was now spreading its control over the forest, one that commanded powerful undead and monsters.

Additionally, the two remaining members of the Three Monsters also took notice of it's growing presence and began to amass an army of their own combined might to drive this new power out. The Gigu Tribe opted to escape the forest, splitting up before war broke out, but in their weaken state, they soon fell prey to adventurers and the rest got captured by the Giant of the East. Word of the rising power was brought to Carne Village by a hobgoblin named Agu.

The Ruler of Conspiracy Arc
According to Ainz, the Fake Nazarick, or perhaps a resource depot as he described it had been completed for now. Aura’s next task was to conceal the fortress and strengthen its defenses as a bunker.

Trivia

 * It was originally unnamed, but the inhabitants in the Great Forest of Tob had given it one.
 * The Monument of Ruin was also used to store all manner of supplies and resources. Since Jircniv knows the location of Nazarick, Ainz decided that the original purpose of the building was useless, so it instead has become a bunker in case that Nazarick is conquered.