An altar is an area in the map, Twisted Treeline. There are 2 altars which are on opposite sides of the map. These altars are captured by simply standing on top of it for roughly 8 seconds. When captured, an altar is sealed for 90 seconds and provides the capturing team a buff that would help in the games progress.
When one altar is captured, it will grant +3 gold on kills, much like Loaded Dice. When two altars are captured it will also grant +10% attack damage and ability power. Altars also give vision of themselves to both teams.
The altars each have their own sets of quotes upon being captured. Some of these quotes are specific to champions aligned with the Shadow Isles.
The amount captured decays over time (if a capture is interrupted) at the same rate as it increased regardless of how many champions opposed to the capture are present. A capture can be halted by having a champion opposed to the capturing team on the altar, but this only pauses the capture; in order to reverse the capture, the capturing champion(s) must be knocked off the altar. Capturing is unaffected by recalling (in that, a champion recall while capturing).
Unlike the Dominion towers, the capturing champion taking damage does not interrupt. To stop the seize of the altar an opposing champion must stand upon the altar in order to have an effect on the capture.
The phrase "Alas, poor Yorick" is a reference to the play Hamlet by William Shakespeare.
The phrase "Bring out your dead! Bring out your dead!" is a reference to the movie Monty Python and the Holy Grail.
The west altar behaves agressivly against the Shadow Isles Champions , reminding them their apparent errors , mocking them , and questioning them.
On the other hand the east altar behaves friendly to them , asking them for help , glorifying them and offering them his service.
The West altar is often referred to as the "Lady" and the east altar as the "Lord" due to the images that appear after capturing them and their voices.
Twisted Fate'sGate is a useful way to capture both altars in quick succession because its range is slightly larger than the distance between the two altars.
The western altar's quote, "This place was once so... beautiful.", suggests that the Shadow Isles, and all its inhabitants, were transformed by the some past event, possibly the Rune wars.
The two spirits that appear when an altar is captured are husband and wife. They died there 1,000 years ago.
The reason why Evelynn has no quotes coming from the altars is that Riot didn't want to give too much information about her lore. But they did, however, confirm that she did come from the Shadow Isles.