The pitch-black sewers.
A few hundred years ago, after the Empire was just established, the Wise Prime Minister, Halva Karabeyan, proposed that they should adopt the sewage system of the Capital of Triumph—the capital of the two Empires—and that it should be built as soon as possible. He had suggested this when the capital was newly built, the construction of the Eternal Star City was still unset, and the sewage work was underway. Tormond the First, who was old by then, pondered over this for an entire day before he launched the grand project that caused the Six Great Clans to groan endlessly about it, but earned the praise and acknowledgement of the citizens in the later generations.
Tormond only had one condition: the underground area of Renaissance Palace, which was being reconstructed at the time, was to be made a restricted zone of the sewage system.