Indiana Jones and His Desktop Adventures

Alien Abduction:
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As mentioned in the Trivia section, one of the main quests possible
in Indy DA is to retrieve a strange idol which frightens the local 
townsfolk. When Indy enters a hidden temple and finds the idol in 
question, it turns out to be C-3PO's head.

There's an Easter Egg that can be achieved on this quest to give you
a different (and even weirder) ending, though.

There are three screens of scrubby desert that Indy must walk through
before reaching the temple with the "idol." To activate the Egg, you 
just have to wait around in these screens for a while (for example, 
by taking the time to kill every single animal in them) instead of 
immediately rushing for the temple.

When you finally press on, instead of locating the temple with 
Threepio's head, you will find a boat, which you can use to cross a
lake. Next, there is a Y-shaped rut in the ground, along with three
stone blocks. Move the blocks to the endpoints of the Y-shaped 
marking.

At this point Indy will be kidnapped by an alien, who mentions in 
passing that Indy obviously has too much time on his hands. The 
quest ends with the spaceship leaving Earth.


Easter Egg:
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Incidentally, this Easter Egg is referenced by another Easter Egg in
LucasArts' other desktop adventure game, Yoda Stories. During the 
"Cloning Machine" quest, Luke Skywalker has the opportunity to find 
the same alien spaceship, along with Indy himself, who thinks Luke 
is "some kind of test pilot."