Waystones are your map keys, ranging Tier I-XVI (T16 only via corrupting a T15)
As of 0.5.0 Waystones must be identified before they can be run
Use Precursor Towers to reveal the Atlas and apply Tablets to nearby maps
The Atlas Passive Tree has 300+ nodes and can be freely re-allocated
Don't waste currency over-rolling low-tier maps
Run Citadels carefully - they lead toward pinnacle bosses