Entering the lower level of the Royal Vaults, the heroes encounter a drow priestess of Phaervorul, rescue the soldier, and battle three drider thralls controlled by a familiar pair of mindflayers...
Valeth V'riza, drow priestess thrall lvl 15 - 1200
3 drider fanglords including Ingarl lvl 14 - 3000
Vurin & Turin, Mindflayer Masterminds lvl 18 elite - 8000
Total: 12,200/4.5=2711 XP each.
Rescue Adakmi soldier, level 14 minor quest - +250 each
Total: 2961+105,366=108327 XP
Need 119,000 for 19th level