Invasion... Level 1: Contamination

Invasion... Level 1: Contamination is a single-level PWAD for Doom that was released in 1994. It was designed by Andy Chen and Claude Martins. It was followed by Invasion... Level 2: The Upper Decks.

Secrets

 * 1) Go through the first door and turn right.  Near the first armor bonus you reach are two alcoves.  Pressing the western one opens up a secret door opposite leading to a passage with a shotgun guy and two health bonuses (on medium and hard skills only), and a megaarmor which lies on a teleporter to the south-east area.  Both the passage to the teleporter and the teleporter itself count as secrets. (sector 27)
 * 2) See #1.  It is not possible to receive credit for this secret as the player teleports before stepping on the sector. (sector 28)
 * 3) From the blue key, head east then south.  Continue through a fake wall, at the end of which is a soul sphere. (sector 118)
 * 4) Heading north from the blue key area, there are two passages to the west.  Between them is a fake wall, through which is a partial invisibility and a lift leading up to a berserk. (sector 122)
 * 5) The room with the teleporters leading to the red key area has a secret door on its north wall leading via a second door and a lift to the yellow key and a box of shells.  Both the sector between the doors and the yellow key sector count as secrets. (sector 256)
 * 6) See #5. (sector 179)
 * 7) Head north from the blue key area then turn right at the end and right at the end of that path.  Immediately on the left is a fake wall through which is a shotgun guy on a platform (on medium and hard skills) and a nukage pit down below, which contains a chainsaw as well as (on medium and hard skills) a medikit and a spectre (two on hard skill).  There is a switch which causes the platform to lower, allowing you to jump across and out of this area.  Note that entering this area activates a crushing ceiling. (sector 285)

Current records
The records for the map at the Doomed Speed Demos Archive are:

Things
This level contains the following numbers of things per skill level: