Siberys Dragonmark of Warding

You have advantage on Intelligence (Investigation) checks and on any ability check made using thieves' tools. In addition, you can cast the Mordenkainen's private sanctum or the forbiddance spell without expending a spell slot or requiring material components. When you cast the forbiddance spell in this way, it protects up to 900 square feet of floor space to a height of 30 feet above the floor. Once you do so, you can't cast either spell in this way again until you finish a long rest. Intelligence is your spellcasting ability for these spells.