The Sleeper sculpture, the names Arkford & Nyarsal, and the pentagram you see during the summoning camvator scene are references to H. P. Lovecraft's Cthulhu Mythos.
The strange exhibit called Transient Audio Cascade Oscillator in the museum is a remake of an item that appears several times in the game Anachronox. In Anachronox TACO stands for Totally Arbitrary Collectible Object, and it's a parody on the numerous collect-all-items quests found in RPGs.
The Bones of Zog found in the museum appeared several times in the old Ultima RPGs (also as museum exhibits).
The museum's exterior is partially based on the Smithsonian in Washington DC.
The SW tower's clock face and its hands are based on photographs of the "Zytglogge" in Bern, Switzerland. The clock should approximately run in real-time, starting at 11 p.m.
The fish fountain seen in Arkford is based on a photograph I took of a fountain near where I live.
The numbers Keeper Lennard gave the inventor as Marten (note found in the inventor's tower, top floor) are from the TV series Lost.
Lisa Wigglesworth's distorted hairdo is a rather obscure tribute to Shodan.
The poster "See Colossal Cave, XYZZY Travel Bureau" is a reference to Adventure, the first adventure game.
Alarius Jewels (and the secret found inside) is a refrence to Jeweler Alarius whose skeleton can be found in Ominous Bequest.
Also, the rotating, twinkling ring in the jewelry store's display window is a light jab at Deadly Shadows' loot glint.
The goblet found in the Hammerites' quarters does resemble the Holy Grail from Indy 3 quite a bit. Though, when you drink from it, you just "die" and don't age several hundred years.
There's another way into the museum without you having to crawl through the sewers first: Just stack two crates on the wall south of the cemetery and jump inside. Sooner or later you'll have to enter the sewers, though, as there's no other way to reach the fountain underground.
The idea for the Horn of Quintus subquest came to me after I had played three FMs in a row where one of the mission objectives had been to find the horn. I thought it'd be fun to come up with an explanation for the horn's frequent appearance.
When you look at the hieroglyph walls in the baths area there's a vertical panel that sums up the story, from the day the seafaring merchants found the island to the moment Garrett arrived through the portal.
The Looking Glass logo can also be seen on the same walls.
To record the mummy sounds I did an undead impression while having paper tissues in my mouth.
If you're wondering what the heck the title picture is supposed to show, enter the tomb where the hammer Draeworek is located, walk right underneath it into the water and then look up.
The plot about the Book of Souls containing an even bigger evil than the necromancer Kadar was initially explained in Ominous Bequest in one of the last readables. However, I felt the story grew too unwieldy, so I scrapped that and left it for (much) later.
... trapping yourself in the first prison cell in the City Watch Station?
... turning around and going back where you just came from right after you've entered a room with a headless victim inside?
... ending the game prematurely by disabling Ned in the watch tower while he's still waiting for the signal?
... shooting a water arrow at the fiery sword depicted in the stained glass window in the musem?
... entering the hypostyle from the temple after Nyarsal has arrived at the island?