Another unhappy couple are Baelen and Derryth Bonecloak, who can also be found in the Underdark.

Source: https://screenrant.com/baldurs-gate-3-best-romance-npc-couples-bg3/

As they travel through the Underdark, Xenk tells the group that they must avoid the Intellect Devourers, that are drawn to mental acuity.

Source: https://screenrant.com/dungeons-dragons-honor-among-thieves-moments-hidden-game-meanings/

Both women can be met in the Underdark and have been captured as slaves by the duergar.

Source: https://screenrant.com/baldurs-gate-3-best-romance-npc-couples-bg3/

The gray-skinned dwarves of the Underdark, the duergar have an alliance with Themberchaud, whom they provide with food.

Source: https://screenrant.com/dungeons-dragons-honor-among-thieves-characters-cameos/

Themberchaud makes his home in the Underdark, a key location in the Forgotten Realms campaign setting.

Source: https://screenrant.com/dungeons-dragons-movie-themberchaud-szass-tam-explained/

We do multiple ventures in Icewind Dale, our current module setting going through the Underdark.

Source: https://www.cbr.com/neverwinter-forgotton-realms-ed-greenwood-brett-norton-interview/