2 players. Player One plays a drone on a chosen note. Player Two uses a choice of one of the following scales to create a slow, chant-like melody:
Dorian mode: 1 2 b3 4 5 6 b7
Phrygian mode: 1 b2 b3 4 5 b6 b7
Aeolian mode: 1 2 b3 4 5 b6 b7
Play in the most resonant space you can find (e.g. church, large concert hall, parking garage, basketball arena, aircraft hanger, Grand Canyon, etc.). Go on for a long time.
Idea: Instead of just one player on the drone, have 2, 3, 4 or more.
Variation: Instead of one soloist, have two. Listen to each other, steal a lot.