As a dark demon realm, Royal Makai has the usual black trees, glowing plants, and perpetual night that characterise other lands of its type. Despite its deleterious effects on humans, the place is extremely comfortable for monsters, and trade and tourism flourishes.
The Demon Lord's fortress sits at the center of Royal Makai; a vast and foreboding castle disproportionately filled with bedrooms. It is here that the Demon Lord and her husband spend most of their time having sex, trying to build the power to break the original Chief God's settings. Around the fortress lies the Succubus Castle Town, the largest city in the world. It's mostly a red light district, but also hosts the Royal Demon Art Museum and the headquarters of the Sabbath. Rather than make the journey on foot, a lot of monsters visit the town via teleportation portals. Outside the Castle Town, Royal Makai also hosts a vast Tentacle Forest.
Although it is in the deepest and most dangerous Demon Realm, the armies of the Order have succeeded in attacking the Castle Town on multiple occasions. The Demon Lord's fortress itself, however, has never been breached by the Chief God's forces.
An immense monster realm that can even be said to be the main stronghold of the monsters. The demon lord's citadel, “demon lord's castle” is located there. In its center there is a city centered around the enormous Demon Lord's castle which is more enormous than any other city in all the human world and monster realms. Technically it's classified as one of the dark monster realms. The scenery is also mostly the same, but perhaps because of the monster lord's presence, the magical energy is so highly condensed that a normal dark monster realm doesn't even compare. It goes without saying that ordinary humans cannot resist monsterisation, but not even veteran heroes can. The monsters that dwell in this monster realm filled with the greatest concentration of monster mana, grow even more powerful and lustful than the monsters of other monster realms which are in turn more powerful than the monsters in the human world, plus, as previously mentioned, the air has the greatest concentration of monster mana, so humans who enter this monster realm are definitely not coming back out as humans.
The royal monster realm is also called “deepest part of the monster realm”, but there is much intermingling with other monster realms, and monster-friendly states, etc. that is, all countries except the anti-monster states under the control of the order's forces. There are various amusement facilities such as an enormous art gallery, a colosseum, etc. and the magical research institute which is owned by Sabbath.
There are also overwhelmingly huge shopping districts, etc. that can't all be seen during a single stay,
so there are lots of visitors from outside. The Demon Lord also seems to value cultural exchange with every monster realm, every nation, and every region. While the order's soldiers desperately march on, portals (teleportation spells) are periodically being set up that connect to each monster realm and monster-friendly state.
I recommend living there permanently, but even if that's not your intent, I recommend that you at least go there once with your husband and see it.