Domu is an ancient library in Ninjago. It houses several important documents, including Master Yang's Airjitzu scrolls.
At one point, Ronin broke into the library and stole the scroll of Airjitzu.
Weeks later, Morro visited the library seeking the scrolls, but stormed out after he learned of the theft.
Wu visited Domu to try and figure out what Clouse was planning. There, he encountered Nadakhan.
Lloyd and Zane came to find out why Wu came to Domu when they discovered he was researching Nadakhan. Here, they were encountered and captured by Ronin.
LEGO Ninjago: Masters of Spinjitzu
Season 5: Possession
Season 6: Skybound