Haven't a clue. Wales went there before the rugby world cup for training and spent the time lifting tractor tires (although I suspect that they are available more locally) - maybe they're doing this.
Maybe RDM decided there's no way anyone is going to touch some of the players that he wants rid of and some parts of Austria are pretty remote and Mountainous obviously so - easy to "lose" people. He could possibly have devised a mountaineering exercise where the players are split into groups and have to fend for themselves and find their way back to a base camp over a number of days.
Gabby, Lescott, Richards, Bacuna and Guzan are all in the one group. And hey presto, we've "lost" a group of squad members who nobody wants. That's a shame.....
More likely but less satisfactory: fitness, team building, and assess the current squad members as mentioned above.