Interval trainings are never fun! That has been my view ever since I started running. They are great to built your conditioning and strengthen your heart, but they are done out of necessity and not because they are fun.
This is of course my opinion, and others might have a totally different view. But I am more fond of running with music in my ears, looking at all the beautiful things in nature than struggling to breath after only just a couple of minutes.
I have found one training session that might change my view though. It's not strictly a pure condition interval, but closer to tempo training. It's a interval session that takes an hour to finish and that has active breaks, meaning you never stop running at any point.
Because this isn't the craziest paced interval, I usually only have about 10 minutes easy warm up before I start the intervals. As the runs are progressive they will warm you up plenty.
Interval 1: Every interval is from 8-12 minutes, with a five minute break inbetween. I usually run 10 minute intervals at the moment and try to finish the first interval at about 165-170 bpm in pulse. All the pulse data in this article is based on how my pulse works, and you might have to try it out for yourself to get the right values that fit you.
I always try to run with at least 2% incline on treadmills, as this feels more like running outside.
Active break for five minutes. Even though you are still running during the breaks, the focus here is more at getting the pulse down and drink. Run slow enough that you are sure that your pulse will decrease significantly.
Interval 2: Repeat interval 1, but at a marginally higher pace. At the end of this interval your heart rate should be between 170-175 bpm.
Active break for five minutes with the same pace as earlier.
Interval 3: Increase the speed marginally again from interval 2 and you should end up at between 175-180.
At this active break you should struggle getting your heart rate down as much as before. Your body is getting very tired and you should just get ready for a hard mental challenge.
Interval 4: If you are able to do it then increase the pace a tiny bit again to get the most out of this session. Your heart rate should get past 180 now as you finish the last leg.
After the last interval it might be smart to cool down with 5-10 minutes of easy running before you go and stretch.
I usually do this on a treadmill. What is most important when doing so is to find one treadmill and use it every time as there are huge differences between mills of same type.
My usual pace is 12.6 km/t at 2% for the first interval with a 0.2 increase in pace for every intervall. That way I end up at 13.2 km/t. My active breaks are at 8 km/t. Be aware that these are the numbers I use, and you should use your heart rate underway in order to find the correct pace for you.
As a last notice. This is classified as a hard workout and should not be overdone. Too many of these workouts per week will increase the chance of overtraining. My rule is to do two hard workouts per week.