Just spend a few weeks with the famaly in Senegal. Yeap you heard right Senegal: dessert, palmtrees, saltlakes, Baobab forests, beaches, sea but no mountains. Vacation doesn't necessarely means that all training comes to a halt on the contrary. You don't really need mountains to train , it helps but it is not a must. I did everey day two trainingsesions. Mostly an early morning beach run of about an hour togheter with he local wrestlers and soccerplayer. It was astonishing to see how many Senegalese run the beaches in the morning and they don't run on het hard wet surface along the waterline but in the damp loose sand above the high tide mark. So that's what I did too; You got to blend in and I admit, it was a great exercise. You need to put so much more effort into it and it is good for your balance too. Those first runs were really exhausting but as you progress you improve the technique and it is really fun. Afternoons were mostly reserved for a fitness session : upperbody training , stepping or spinning and of course a lot of time swimming in the pool or the sea and a lot of resting equally important. So wherever you go there are always opportunities to work on your physical condition.