6 miles -- I told myself "It's just 6 miles." I truly believe that, too.
I did an out-and-back. It was, of course, hot and humid. Occasionally, there was a cool breeze. However, each mile got progressively slower. I went from 13:23 to 17:38 with all of the walking I did. My heart rate was pretty high, so I tried to keep it down.
That's really all I have to say about it! I just got it done, by any means necessary (i.e. walking). The weather wore me out; afterwards I took a 2-hour nap!