The Inner Sanctums located in Unseth are a series of abandoned underground tunnel networks used to fight against the Monothe during the Desolate War. It was originally built for smugglers to transport contraband from Monothe into Unseth and vice versa.
During the Desolate War the tunnels were expanded to create an effective tunnel network for sneak attacks into Monothe. The Monothe government has attempted many times to outright destroy the tunnel but the network was much too big and expansive to be blocked off effectively. The expertise of Unseth engineering and relentless retaliation against Monothe troops sent into the tunnel allowed the tunnels to be active throughout the war. The Monothe's lack of knowledge of these tunnels have led to entire platoons becoming lost in the network and dying of starvation.
As a final act the Monothe built a gassing machine capable of pumping enough poison into the tunnels, this specially developed odourless and colourless gas spread especially fast and killed a large portion of Unseth troops stationed within, ensuring that the tunnels had to be blockaded by Unseth to prevent the gas from entering Unseth's surface. The body count of those killed by the gas reached upwards to 500,000 including troops from Monothe but the total body count in the tunnels total reached a figure in the millions.
Even centuries after the war the tunnels still exist but is cordoned and quarantined for safety as the gas is still potent and has not yet dissipated, however refugees and smugglers have been known to attempt to pass through the tunnels for a quick passage without prying eyes.