The "n00b bridge" is an infamous room in Brinstar in Super Metroid. It is a long corridor in the jungle section of Brinstar, with a "bridge" that consists of Pit Blocks, and a ceiling lined with spikes. Apart from this, the only unique feature to the room is the abundance of red and pink bloomed flowers.
The bridge cannot easily be crossed without using the dash button for speed. Barring Sequence Breaking, it is the first place in the game where the dash button is required to progress (as intended by the developers). Many new players have found themselves unable to figure this out; hence the fan name "n00b bridge".
The Green Door on the right side of the room leads to the "Red Tower", while the Blue Door on the left leads to more of Brinstar, but it cannot be accessed due to the presence of a blue Shutter in the other room.
One of the dream readings by Ariadne Yuko in the Japanese Super Metroid guide, "A Bridge Too Far", appears to be based on this room. Samus describes being unable to cross a bridge on Zebes. Yuko suggests that the bridge is preventing her from growing into adulthood, and recommends that Samus try training herself to be more feminine.
There are a few ways to cross the bridge without the dash button. In the PAL version of Super Metroid, it is possible to roll across the entire bridge without using the Mockball, although it requires several tries if one is not experienced with the technique. This is due to Samus being sped up to account for the PAL convention of 50 frames per second. The other method is to jump repeatedly across the bridge, though this is both difficult and quite dangerous to pull off because of the very strict timing and the spikes directly above. Both of these tricks are significantly harder than simply dashing across the bridge, however.