I used to sand sprints , until i fractured my ankle
when i'm out on the bike , at the back of the local lake are a flight of stairs and a hill , not very high hill , but it's a hill (man made) , so i throw the bike on my back , the bike weighs about 6kgs , so run up and down the hill and stairs a few times
about once a week i do sprints at the soccer field which is just around the corner from me