Nexus

The Nexus is the main building on a map, and is symbolized by a giant crystal. The nexus is the most important structure on the battlefield, In order to win a game, the opposing team's Nexus must be destroyed.

Classic mode
Nexus is the source of the minion armies. The team’s two weakest turrets protect the Nexus (one on The Twisted Treeline). These turrets regenerate health over time, which means in order to be destroyed they need to be attacked continously.
 * The Nexus has 5500hp and 25 hp/5. It has no armor or magic resistance.

The turrets guarding the Nexus will be invulnerable if the team has all of its inhibitors up, so in order to destroy the Nexus you need to destroy at least 1 inhibitor. Destroying more of them will make it easier for your team to push. The Nexus is also invulnerable until both towers guarding it are destroyed. Make sure you have a strong minion army with you before you think about engaging the enemy’s nexus, as it won't be easy to do it alone. However, if you manage to destroy the enemy nexus, their backbone of their war machine will be broken, and you will be declared victorious.

Take heed: The Champion's Spawning Pool is always positioned close to the Nexus, so expect fast enemy Champion reinforcements. The placement of the Spawning Pool also allows Champions to quickly regenerate their health and mana, allowing them to run right back into the fray. Killing the Champion is the only proper way to stop this hit-run-recover cycle, at least until the Champion respawns. Even if the Champion escapes back to the Spawning Pool by a hair's breadth, he will still require time to fully regenerate, which should be taken advantage of while sieging either the Nexus or the Inner Turrets. On The Twisted Treeline, the Summoner Platform is positioned very close to where minion waves pass by. As a result, minion waves will follow enemy champions onto the Summoner Platform if the Champion positions himself correctly. This is an effective tactic for disposing of waves with Super Minions.

Dominion mode
In Dominion, the nexus is untargetable, but its health is reducing under 2 circumstances:
 * If the player team has taken control of more capture points than the enemy team, the enemy nexus will continuously losing health until the numbers of controlled capture points of both sides are even. The more controlled points, the faster the enemy nexus saps.
 * When an enemy champion is slain, the enemy nexus health will be reduced by a flat amount of 2.

The health of nexus is reported when reduced to 75%, 50% and 25%.

Trivia

 * The League Champion, is currently bound to a nexus fragment, trapping him in the physical world.
 * Destroying the Nexus awards 50 Gold.