Is there anything past the flagpole in Super Mario Bros?

As we know it is possible to jump over the flagpole in Super Mario Bros, are there any secrets or easter eggs beyond them? Growing up I heard rumors that there was a secret pipe if you ran far enough, however I'm skeptical now that I'm older since it appears that it's more of an unintended exploit than a "secret".

This question applies to the original or any remakes of the original.

Solution 1:

The ability to jump over the flagpole is a glitch. As per the Super Mario Wiki:

In some levels, it is possible to jump over the flagpole. Beyond the flag pole is nothing but an endless path. There is nothing to do; all that can be done is wait for the timer to get to zero.

[...]

[...] this glitch was fixed in the SNES version of the game.

There is no secret pipe and while the regular game will just have the timer run out on the player, when using a cheat to disable the timer the player can run far enough to cause the game to glitch.

[...] if the player were to disable the timer using a cheat code and continuing running, they will eventually reach an area where the background and platform sprites become jumbled.