PoE2's endgame is built on Waystones and the Atlas, not PoE1-style Watchstones. Waystones are map keys consumed in the Map Device and range Tier I-XVI (I-V white, VI-X yellow, XI-XV red; T16 only by corrupting a T15 with a Vaal Orb).
As of 0.5.0, Waystones must be identified before they can be used.
Precursor Towers reveal the surrounding Atlas and let you apply Tablets to inject league mechanics into nearby maps.
The Atlas Passive Tree has 300+ nodes (around 301) and is fully allocatable in 0.5.0 with free re-allocation. It is reorganised so each league mechanic (Breach, Delirium, Abyss, Expedition, Ritual) has its own sub-tree, questline and pinnacle boss.
0.5.0 added the Precursor Fortress (rises after your first Tower; its maps grant Atlas passive points and culminate in the Arbiter of Ash) and Masters of the Atlas (Doryani, Hilda, Jado), each offering 12 nodes of which 4 are selectable.
Citadels are rare maps that yield Crisis Fragments toward the Burning Monolith. 0.5.0 added two new Citadel maps and bosses dropping keys to the new pinnacle, the Arbiter of Divinity.
0.5.5 made Expeditions a core Atlas mechanic, including in Standard (you can find them from Act 4 onwards in the campaign, and the Verisium Anvil unlocks with The Runeseeker quest in Act 4). In the Forbidden Rites league only, Sacred Blooms from Rituals can add the Viridian Wildwood to a cluster of Atlas Maps. A Grand Mirror's Delirium Fog now spreads to 10 Maps, reduced from 8-14 on lower-Tier Maps and 10-16 on high-Tier Maps.