Favorite swim workout?

My favorite swim workout is the Rebecca Adlington set - 4 rounds of 50, 100, 150, 200, 250 (off a one-minute base) with a 300m easy swim in between each round. It's brutal, but it's also really satisfying.
 
Transcript: "Oh, favorite swim workout. Well, I've been a swimmer pretty much my whole life. So I feel like if you could kind of say make up a swim session, it's one of my top skills. It's just like, I'll write a swim workout. But I think one of my favorite sessions is actually quite a hard high-intensity session. And we used to do it as swimmers, and it was actually called the Rebecca Adlington set. And it's basically you do a 50, 100, 150, 200, 250 or as hard as you can, and they're off a one-minute base for each 50. So you get more rest as it goes on, but it kind of lets the lactate build up and develop. And in between each round, you get a 300 meter easy swim, and you do that four times. And I promise that by the fourth round, your arms are like balloons, and you just can't feel anything. But I kind of love that sickening pain of the session. So yeah, that is definitely my favorite swim workout. But it is brutal."