Nightfall

Nightfall (stylised as NIGHTFALL!!!!) is a single-level PWAD for Doom that was released in 1994. It was designed by Josh Fallon.

Secrets

 * 1) Entering the yellow key area causes a chasm to raise.  This chasm can be lowered temporarily by pressing a switch on the westernmost pillar, allowing access to a room to the north of the chasm containing a chainsaw and two shotgun guys. (sector 83)
 * 2) In the west of the level is a large room with a large square blood pit.  On the east side is an arrow on the floor.  Approaching the arrow causes a platform next to the arrow to rise.  When it has finished rising, step on it.  This causes another platform to rise ahead of you.  When this platform has finished rising, step onto it and a BFG9000 will be revealed in front of you.  Note that if you do not wait for either of the first two platforms to finish rising before you step on them, the next platforms will not raise to the full height, making it impossible to obtain this secret without becoming trapped. (sector 197)
 * 3) In the red key room there is a secret door on the east wall (marked with a different texture) leading to a spectre and a light amplification visor. (sector 291)
 * 4) Go through the door opened by pressing the switch behind the three locked doors.  You will go down two lifts - from the second one is it possible to jump into the northern alcove at the bottom.  The back wall of this alcove is fake, and it leads to an energy cell pack. (sector 414)
 * 5) In the north is a dark room with several four-sided structures.  All have silver textures apart from the northern wall of one structure in the north-east, which is red.  Pressing this red wall opens up a nearby door leading to two lost souls and a light amplification visor. Note that this door can only be opened once from the outside. (sector 416)

Bugs
Near secret #5 there are two (on easy and medium skills) or four (on hard skill) lost souls that are meant to teleport in. However, as they are flagged as deaf and can never see the player, they are never woken up and thus do not teleport in and thus cannot be killed. As they are flagged as monsters in version 1.2 of Doom, or when using -complevel 0 of PrBoom+, 100% kills is impossible in this version.

There are also two (on easy and medium skills) or four (on hard skill) spectres that are meant to teleport in when the yellow key is obtained. On version 1.9 or Ultimate Doom, or using -complevel 3 of PrBoom+, these monsters do not teleport in, making 100% kills impossible in these versions as well.

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

Player spawns
This level contains four spawn points:
 * 1) facing east. (thing 300)
 * 2) facing north. (thing 301)
 * 3) facing south-west. (thing 302)
 * 4) facing north. (thing 303)

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

Technical information
The sky texture was later used in Doomsday of UAC.