I did a lovely hill session today. Lovely in the sense that it was Kenyan hills (where you just keep going up and down, trying to maintain as even a rhythm as possible) so you get into a sort of karmic zen mindspace where you just keep going and going. I was so mentally chilled (if physically boiling in the warm sun) that I lost count. I meant to do 10 reps and ended up doing 11. The reps took 2.05 miles - so I reckon that's about a mile up and a mile down.
That'll do nicely.