The Frey Clan had been built with simple walls and corridors at its founding but since then, Lind had been expanding his skills to create spaces attached to certain rooms. He had already created a primitive Inheritance before but had scrapped it once he returned to the Heaven Realm lands.
Heaven Realm Inheritances were not overly complicated and usually were legacy items for clans or sects.
It was essentially what he created for 6 elementals as his goal had been to help them achieve ascendance to the Immortal Realm.
It was useful and allowed future generations to grow but a true Inheritance was much more robust. He had thus been practicing on a smaller scale but it was just playing with inverted space.
The most impressive creation he had was one no one noticed.
The Clan library was seemingly opened to all the family or special guests but no one had noticed that the room did not actually exist.