Here's an "active recovery" workout my masters group did on Sunday. Loved it -- my favorite so far, I think!

1000 warm up
(400 stroke, 300 pull, 200 kick, 100 free)

12 x 50 @ 1:10

4x25 @ :30
100 easy (very easy; go right from the 25s into this, your active recovery)
4x50 @ 1:00
200 easy
4X75 @ 1:30
300 easy
4X100 @ 2:00
400 easy

8 x 25 @ :30, ascending

3600 total