The Black Pits is a series of sequentially more difficult arena style battles, spread across 3 tiers, 5 battles in each, for a total of 15 excluding the opening battle. Gameplay is roughly 8 hours for first-time playthrough, 2 to 3 hours if importing strong characters.
Characters may reach roughly level 10 (level 9 for high experience requirement classes and level 11 for low experience requirement classes). You may export your characters anytime then start the main games with them. They'll remain at the levels at the time of exportation but their experience cap will be reduced to 161,000 in BG1 or 500,000 in SoD.
- Bhaalspawn abilities and Find Familiar spell can not be used in BP1, characters with those spells will have them erased when imported into BP1.
- BP1 Characters exported into Siege of Dragonspear and Baldur's Gate II: Enhanced Edition will gain Bhaalspawn abilities randomly according to alignments.
Talk to Baeloth the Entertainer (drow) to enter the arena battle, You may pre-buff your party before each fight, you may also repeat previously completed battles which will net you additional Gold and XP.
There're also Thardek the duergar, Gorch the duergar, Magda the duergar, Dingar the Mad (duergar) Bellowgulp Bluefingers (duergar), Xithiss the mind flayer, Elan Garaq the rakshasa, Brendak the duergar, and Devlin Taralon the elf. These NPCs have stores from which you can buy various weapons, armors, accessories, spells, wands and consumable items. They'll have their own perspectives in serving Baeloth and minor stories, Elan Garaq and Thardek will fight alongside Baeloth in the final battle. The combatants of 5th, 10th and 15th battle will also appear in the prison cells.
You can not attack any of those NPCs.