I think the farthest point in MK would be either Haunted Mansion or toontown. For ToonTOwn, I'd take the train and save some time on my feet. For Haunted Mansion, it's probably easier to walk to the enterance (you'd have to either walk to Splash Mountain or ToonTown to get the train). It would probably be faster to walk through Liberty Square to the castle then down main street, maybe takes 10 minutes. THe boat launch is right outside the gate, probably about 1-2 minutes to walk there.