Without further ado, here's what you'll get to choose from if you're choosing to suffer out there in the great outdoors.

1. O1: 4 x 400 meter intervals. Ideally you've got a track for these but any measured course of approximately this distance will suffice, as it is the repeatability that is most critical. You'll need to specify an interval on which to begin each 400 and a 'time' in which to complete each lap (target time). For example, for your first go you might aim to leave every 3 minutes, completing each lap in two minutes and resting the remainder. These should all be hard. Consistency is key--keeping the first one 'light and fast' in your head and then hanging on for dear life as you push deeper and deeper to make the remaining intervals. Because this is a Baseline Workout each time you revisit it you'll aim to decrease some parameter--either your target time or your starting interval. For a second go (using the example above) this might involve aiming to start each interval after 2:45, or better yet, do this and finish each lap in 1:45. If you're new to intervals you'll probably find you progress very quickly between subsequent workouts.
2. O2: 8x200 meter intervals. Very similar to the above, but of course the target time and interval times will be less. The overall workout should take roughly the same time, give or take.
3. O3: Hill repeats: Find a short(ish) hill that takes you from between 30 seconds and two(ish) minutes to run up at a moderate pace when you are absolutely fresh. This 'moderate pace time is your leaving interval and your target time. Starting at the top, run down to the bottom, staying loose and fast (downhill running takes practice too!). At the bottom, once your interval time is up, head up the hill. Get to the top (hopefully beating your target time, rest it's remainder, and head back down. Unlike in the previous workout, you don't actually get much rest on this one--a few seconds at most at the bottom of the hill. You'll need to focus on getting your breathing in check and HR back under control while simultaneously moving efficiently back down the hill in order to be successful, great attributes for the whole 'relentless forward progress' idea that will be so important during long runs. Decide on the number or intervals to do ahead of time, ideally somewhere between 2 and 10 so that the whole workout takes roughly 10-15 minutes. Trust me, it'll be long enough. Example--it takes me about 2:30 to run up my gravel driveway 'comfortably'. For this workout I do 2-3 intervals, with interval time and target paces both at 2:30. I 'warm up' on that first run down, have about 20 seconds rest, then head back up.