At the north end of Reithwin in the Shadow-Cursed Lands of Baldur's Gate 3 is a mausoleum. Hidden beneath this mausoleum is a massive temple, the Gauntlet of Shar. Shadowheart has every reason to complete this gauntlet, but even players who don't use her will need to explore this location.
Baldur's Gate 3: How to Complete the Gauntlet of Shar
Even without Shadowheart, Baldur's Gate 3 players will need to solve the difficult Gauntlet of Shar to beat Act 2.