The adventure mode is basically the Shandalar. It was added only a couple years ago by a single developer[0]. But it had excellent support since, especially in 2023. And right now it's very feature-rich with a lot of dungeons, bosses, artifacts, simple quest system, etc. New stuff comes out every month.
[0] - https://www.slightlymagic.net/forum/viewtopic.php?f=26&t=304...