Strongholds

Strongholds are essential to the game because they are the only way to get to the End.

To find one you need to right click with eyes of ender and they will go in the direction of the nearest stronghold. After a little while, they will go directly into the ground, and then you dig straight down and watch out for cobblestone and mossy cobblestone because that are what the stronghold's walls are made of. Once you get into it, you have to find the end portal room and right click on the end portal frame with eyes of ender. All you have to do now, is jump in to the portal and be instantly teleported to the End (see The End).