Demon King

Underground Fortress → Underground City

Requirements met. After paying the source essence and materials, Civilization's evolution progress bar naturally appeared on the building panel.

This kind of upgrade operation, where meeting the requirements led directly to an upgrade—

Although Linsey had only reached out and pressed a button, once it was done, he felt an exceptionally smooth sense of satisfaction.

It was as though he were really in a game.

It felt as satisfying as using the main base's resources to rapidly advance construction at a secondary base.

Linsey looked ahead.

Black, obsidian-like stone was gradually enclosing the Town Hall before him. Though it was not yet complete, its solemn and oppressive majesty was already beginning to show.

Linsey nodded in satisfaction.

Then he assigned a task to the girl beside him:

"Vivian, I plan to build a Hero Altar east of the fortress."

"Go call the workers over. This building can be used without a Civilization upgrade, so let's get it built first."

"Okay." Vivian obeyed and left.

Linsey walked east alone and placed the Hero Altar's construction blueprint first.

The workers soon arrived.

The workers trained by the Underground City were called miners.

Besides gathering minerals underground, they could also take on projects such as building cities and excavating Mazes.

And among the three cities Linsey currently managed—

The miners' production speed was basically among the fastest.

With several workers laboring together, the Hero Altar's construction speed was boosted by more than double!

The insectoid soldiers cleaning up the battlefield in the Maze had not yet returned.

Yet a brand-new Hero Altar had already appeared before Linsey.

Like those in the other two cities, the Underground City's Hero Altar was also distinctively styled.

Black, glossy, irregular rocks formed a heptagram-shaped platform upon the ground.

At the heart of