Lazlo!/Antlion Desert - Half-Life 2 Part 15 [Hard]
A troublesome house, roadblocks, lighthouse point, Antlion desert. Poor Lazlo!
This took five full render sequences (at 2.5-3.5 hours a piece, excluding the last two which were closer to 1.5 hours a piece due to switching to Sony's AVC codec) to work properly.