I live in a canyon/ravine here in SOCAL and the walk in any direction is uphill. In one direction it's 20 minutes to the top and then another 10 minutes to the shopping center. Roughly one hour round trip if I don't delay at the shopping center. That 20 minutes uphill gets my heart-rate way up and then another 40 minutes of cruising and cool-down.

Walking distance, even relatively short distances like 3 miles is great, but don't forget swimming. Knowing how to swim and being in good swimming condition lends a lot of confidence to many activities around water.