... arriving in Eeofol, aka The Land of the Giants. The second you set foot in Eeofol after exiting the cave of medusas and behemoths, Archibald contacts you psychically and announces his departure from the pit, and gives you the first blaster.Once you have been to Eeofol, Clanker's Lab is off-limits.
I personally find this an interesting trade-off, because while Clanker's Lab has some hot treasures and reagents galore, Eeofol has all those Genie Lamps and it reloads every six months. (I have a soft spot in my heart for genies.)