On the Concept 2: 
6 min, 5 min, 4 min, 3 min, 2 min, 1 min pyramid / 1 min rest

Pre-set the monitor for 27 minutes. Row six intervals in a pyramid of 6-5-4-3-2-1 minutes, with a minute of rest in between each piece.

Aim to be faster each round. Put in a good warmup and try not to come out too hot.