The Maryland Challenge is a 41.5 mile hike on the entire Maryland portion of the Appalachian Trail…read morein 1 day. It begins at Pen Mar Park (MD/PA border) and ends in Harpers Ferry (MD/WV border). It's rough, but you'll be proud to have pushed yourself to your limits. I found that I went into this thinking I knew a lot of things that turned out not to be true. Some examples: (1) I thought I wouldn't get blisters since I didn't get any when I ran a marathon. (I now believe it's not possible to walk 41 miles without getting blisters.) (2) I thought the difference between mile 21 and mile 41 would be like the difference between getting stabbed once and getting stabbed twice - both would hurt, but there wouldn't be much of a difference between the two. (I now see that the last few miles take things to a whole new level.) (3) I thought my daily runs would be adequate preparation. (I now see that it would have been better to run in those barefoot sneakers, since the trail is littered with sharp 6-inch rocks that stab your feet every time you misstep.) As far as logistics, I do have a few pointers: (1) It's important to plan your start time so that you finish the downhill section of the hike before dark (about mile 35). There's a lot of sharp rocks to stab your feet, not to mention that you don't want to trip off the side of the slope. We hiked in May, and we started at about 4:45AM. (2) There is plenty of water. You shouldn't need to carry more than 1.5 liters at any one time if you have a water filter. If you don't, there's tap water at a few locations, including the original Washington Monument (mile 21) and Gathland State Park (mile 30). We hiked in May (65-70 degrees) with 2.5 liters per person, and didn't need to fill up until the Washington Monument. (Although the sun set a half hour earlier since we hiked in May, I preferred hiking in the cool weather, which meant we had to stop for water less often.) (3) There's plenty of overnight parking across the street from Pen Mar Park (free), and if you're willing to pay $10, you can park at the Amtrak station in Harpers Ferry (about 50 feet from the bridge between Maryland and West Virginia). If you're trying to save $10, the Appalachian Trail Conservancy is 0.60 of a mile from the Amtrak station, and they'll let you park there for free on the weekends if you call ahead. (4) I recommend hiking from Pen Mar Park to Harpers Ferry, because of the thankfully flat tow path in the last 3 miles. However, Pen Mar Park doesn't allow camping. We ended up sleeping in the parking lot across from Pen Mar, by putting down the car seats so that we could set up sleeping pads, sleeping bags, and pillows. This was more comfortable than I expected, and made things logistically easier the next day. Good luck!