I love to swim - hard, and fast. I do four sets of these ladders:
1 lap
pause no less than 10 seconds
2 laps
pause no less than 10 seconds
4 laps
pause no less than 10 seconds
6 laps
pause no less than 10 seconds
4 laps
pause no less than 10 seconds
2 laps
pause no less than 10 seconds
1 lap
pause no less than 10 seconds
5 laps breaststroke
pause no less than 10 seconds
4 laps IM (1 lap butterfly, 1 backstroke, 1 breast stroke, 1 freestyle) and one final lap of cooldown breaststroke.
All that totals to 30 laps for one set. I do that x 4 = 120 laps. And since I'm pausing for a few seconds, it gives a little breath back so I am able to sprint the whole thing, making it more effective than just swimming the same distance straight without pause.