I'm not sure if this is my favorite of all time, but when I look back at the workouts I've done, this one is the tops
I was helping coach at my college alma mater one year. During one workout, the head coach wanted me to pace our top 800m woman. Her workout was supposed to be 4 x 4 x 200 @ 32 with 30 seconds between reps and 4 min between sets. I felt the workout would be too easy, so I did a 4 mile progression run first. Then, during the 5 minute breaks between sets, some of the male distance guys started challenging me to see if I could break 60 for a 400. The whole workout ended up looking like this
4 mile progression to warm up (25 minutes including slow early miles)
4 x 400 @ 32 with 30 seconds rest
100 jog
400 @ 62
100 jog
4x400 @ 32 with 30 seconds rest
100 jog
400@ 61
100 jog
4x400 @ 32 with 30 seconds rest
100 jog
400 @ 60
100 jog
4x200 @32 with 30 seconds rest
The guys tried to get me to attempt another 400, but I was completely fried at that point. I think I jogged an 800 cool down then staggered home.
Funny thing was, that spring, I only managed 4:15 for 1500m. I wasn't really training consistantly, but that workout should have been worth very close to 4:00 for 1500.