25m

25m is the very first level in the game Donkey Kong. 25m is the start of the game, where DK kidnaps Pauline and stomps on the construction site. The result is a basic level, where Barrels roll down the downwards slopes and Jumpman must work his way to the top. This level also introduces Hammers and Trouble Bugs. Beating this level gets to 50m in the original arcade and 75m in the NES version.

Description
Jumpman starts from the bottom left corner and must work his way up via ladders. After a few seconds DK will drop a blue colored barrel, which will set the Oil Barrel on fire, and spawn Trouble Bugs. Donkey Kong will roll barrels down the slanted site, making them somewhat predictable, however some roll down the ladders, broken or not. Note the Hammer near the end, which can be jumped on and used as a weapon against the barrels.

The Game Boy port of it had two layers of platforms removed because of limitations. However, a level that has the exact appearance of the original 25m, with a scrolling screen, appears much later in the game as stage 9-5 in the Tower.