I vaguely remember as a kid being able to squeeze between the pipe and the bricks at the end of a water world that would take you to another water world that never ended. Does anyone recall this or know exactly how to do it? Or is it just a lie I told all of my friends as a kid that has somehow become a reality in my mind over the years?
Yes. You use the warp zone at the end of level 1-2, but instead of getting to it the normal way (jumping on top of the bricks at the top of the screen), you crouch, and hop into the pipe just before the warp zone. This video shows the proper technique:
If you go to level 1-2 then, you need to go by a pipe at the end of the level...make Mario bend down and make Mario jump into the corner of the wall...and yes, it is a glitch. You will go to a place with three pipes...go in the pipe on the left and you will make it to a never-ending water world...also...the never-ending water world is just a glitch world of level 2-1!!!
It can be reached by clipping through the wall to the warp zone at the end of level 1-2.
While this level is known as The Minus World, it's actually level 36-1. It is an endless loop of level 7-2, until the timer runs out.
Warping to level
There are three warp zones in Super Mario Bros.:
- One in level 1-2 to worlds 4, 3, and 2
- One below ground in level 4-2 to world 5
- One above ground in level 4-2 to worlds 8, 7, 6
This is actually just a single warp zone object, adjusted for which zone it depicts.
The tiles above the pipes in the warp zone contain the numbers for the worlds you can travel to, in hexadecimal format. This value is not just used for display purposes, it is used to determine which world you travel to.
The warp zone to world 5 still has three tiles, since it's the same warp zone object. To show only the 5 above the single pipe, the left and right tiles are set to hex value
24, which corresponds to a blank space in the character encoding used in Super Mario Bros. The decimal value is 36.
By clipping through the wall at the end of level 1-2, the warp zone code is not initialised completely, resulting in it thinking it is the warp zone to world 5, yet it has three pipes. As a result, the left and the right pipe lead to world 36, while the middle pipe leads to world 5.
So know we enter a pipe leading to world 36. Entering it will land you in level 36-1, but since 36 still corresponds to hex value
24 and thus a blank space, this renders as
Level 7-2, repeated
Since we're now on our way to world 36, that world needs to be loaded. However, Super Mario Bros. only has 8 worlds. This causes the program to look past the end of the list and use the value it finds there. This value happens to be the one for level 7-2. So the "map" for level 7-2 is loaded.
If level 7-2 itself is loaded, entering the pipe at the end warps us the end of level 7-2. However, since it was loaded incorrectly, the value of where to warp to is never adjusted and remains set to "beginning of level 7-2". That is why entering the pipe just warps us back to the start, repeating until the timer runs out.
This is all explained by YouTube user MagicScrumpy in the video below, on which I based this answer.