The secret level in game design is an optional level hidden from the usual path of exit from a game level. The full game isn’t necessarily incomplete without it. Since players can access complete the entire episode or game it is part of without ever accessing it. They usually give extra bonuses and features in games. Usually, these features that are otherwise inaccessible from the general levels of the game. Secret levels are part of many games.
However, many players may never know their whereabouts or how to access them. Some designs are around themes or gimmicks not found in the real game.
In some cases, secret levels are much more complicated than the actual game. Therefore, they serve as a hidden challenge for elite players to overcome. Also, they are some that have no differences from the main game, but it would seem like the game developers couldn’t figure out which point of the game’s normal progression to fix them. Hence, they make an alternative or secret. Which is a better option than completely deleting them? However, one can still complete the game 100% without the need to complete a secret level. Generally, completing a secret level comes with some reward.
There are different rewards for completing a secret level. Different games offer players various incentives. A google example is God of War. Some standard rewards include a shortcut, some piece of information that completes the story, or a valuable item (e.g., extra armor). Others are trinkets, a congratulation message, a secret revelation that changes the entire cause of the plot, etc. It can be somewhat challenging to spot an entrance to a secret level of different games. However, experienced players know the right places to probe. Usually, you would find secret levels at places in a game where the surroundings hint toward their existence. Otherwise, you can find them by searching for any likely locations.