the simplest (yet effective) workout you can think of

waiter's walk on stairs
do you have access to a flight of stairs? it can be both indoors (the stairs of your condo are perfect for this purpose) or outdoors. i suppose the answer will be affirmative, anyone has access to one or more flights of stairs. well, then you have all you need to perform the simplest (but still extremely effective) cardio workout you can think of. just walk the stairs, up and down. you decide how fast according to your fitness level and, if you're working out on the stairs of your condo you decide how many floors you're going to climb before descending.
going upstairs and then downstairs represents a good example of HIIT, as the ascending phase will be quite intense, whilst the descending phase will work as recovery time. still, even the easy downstairs phase will bring some extra benefits to our health, as the movement required will strengthen our quads and our calves. obviously the upstairs phase will provide a good cardio, but also an effective workout for our glutes. add some weights (in the form of a backpack loaded with water bottles) and it will work your abs too. do it with two heavy bags in your hands and you'll have a powered version of the farmer's walk exercise. pick up something heavy with one hand and hold it over your head keeping your arm fully extended and you'll perform an on-steroids version of the waiter's walk, which will train your balance too (for more on walking with weights, check this previous blog entry).
i really love this type of workout, i do it about once a week. usually my workout sessions take place very early in the morning (between 4.30 and 6.00 AM) and, if i'm using the stairs of my condo, i do it in total darkness, just counting steps. i noticed that it's a good way to improve my overall perception skills. if i want to go high speed i use a headlamp for extra safety, but if i'm going at a normal pace i prefer total darkness. i may use the lights of the condo but they're timed and automatically switch off every minute or so. it's quite annoying and dangerous, as it's extremely easy to loose balance in the same moment when the light is turned off.
this type of workout can be performed in every season, everywhere and by everyone (respecting the limits of our own body, obviously), so there are no excuses to skip a good session of stairs-climbing.