Although PoE just announced a endgame-focused expansion, Echoes of the Atlas also comes with a new PoE Challenge League: Ritual. Ritual is a combat league that pits you against both the arcane powers of the Ritual Altar and escalating waves of monsters, enclosed within a Ritual Circle. 

 

Path of Exile Ritual League

Twisted spires of flesh, blood and sinew now stand scattered across Wraeclast's landscape. Their origins and purposes unknown, they seemingly have a hunger for blood and death and are willing to richly reward those who can sate it.

Ritual is a combat league that pits you against both the arcane powers of the Ritual Altar and escalating waves of monsters, enclosed within a Ritual Circle. Each successive Ritual in an area is harder and offers better rewards.

Ritual Rewards

As you slay monsters during a Ritual, you'll earn Tribute which can be spent on a variety of seductive items and rewards. Among these rewards, you may be offered new Ritual Base Types which pair very powerful implicit mods with challenging drawbacks. You can consume some Tribute to reroll the rewards offered or to defer selected ones until later.

More Gameplay

In the end game, you can obtain tradeable Ritual vessels, which allow you to itemise the monsters from a ritual. You can place up to four vessels in the map device alongside a map to add their monsters to the rituals present in that map, substantially increasing both the difficulty and rewards of those Rituals.  Vessels also substantially increase monster density which can be very rewarding in maxed-out maps that have mechanics like Beyond and Delirium present.