There was a whole thread just on this subject but seemed to have been lost during the downtime.
I think I recall that 4 laps around the promenade was 1.25 miles or a little over a 1/4 mile per lap.
As the above poster stated, most of the deck in outside but at the front and back are areas that you pass through with equipment and such.
The area in the bow of the ship can quite dark at night, so be careful when walking at night. Teenagers also like to hang out in that area after dark because it is pretty secluded, so if you are looking for your teen, check this area out! Sometimes this area is roped off due to maintenance work for periods during the cruise.
Hope this helps.
MJ