I sometimes workout on vacation and sometimes not.
Sometimes, if I workout intensely before, and it's time for a break, or if it's a short trip, I don't worry about working out, especially since I do lots of airport walking (I cart all my own luggage, walk the hallways rather than use the moving sidewalks---unless I'm in a hurry to catch a plane, then I walk on the moving sidewalks, and don't let them carry me along like a passive lump, use stairs, walk places). Taking a break is a good thing, and often allows you to come back with more energy and intensity.
I also make it a point of trying to work walks into my stay, either to scope out the area, or to get around from one place to another.
When I do workout, I use the hotel fitness center, or sometimes do an in-room workout.
Some in-room workouts that have worked well for me:
1) lower body workout with walking lunges (in a particularly wide hotel room I had!), and using gliding discs for various types of lunges and squat variations. The gliding discs fit very easily in a suitcase, even a smaller carry-on, and work great on hotel carpets. You can even use them for challenging push-ups, putting one hand on one disk and moving that hand in and out, or putting each hand on a disc and doing 'flyes' in the push-up position.
2) band/tubing workout: last week, when I was away from home for 3 days to give a workshop, in addition to an hour-long walk one day, I did an in-room resistance tubing workout. I did bicep curls, seated rows (seated on the floor, with tube looped around the leg of the elevated bed, doing both regular rows and high back rows--elbows out to side to hit the upper back more), tricep extensions, overhead presses (kneeling on the band, doing one arm at a time), and front and side delt raises (again, kneeling on the band), as well as push-ups and squats.
I've also done step-ups onto a sturdy chair (not always possible!) and some kickboxing moves (when I'm in a big enough room---on hotel I stay at is kind of a business-person's training session room with no room to do any kind of workout, so I use the nice fitness center).
Depending on where you are, and how long you are staying, you could also buy a day pass for a local gym.
Since it's only 4 days, I say plan activities that allow you to walk alot, and don't sweat not getting in an 'official' workout. Maybe it will be warm enough for biking? Or hiking?
