Matt Lauer -- Un-Vailed in Colorado

TMZ now knows where in the world Matt Lauer is ... skiing his face off in Vail.

As we previously reported ... Matt took the week off from "Today" to spend time with his kids ... smack in the middle of a critical sweeps period ... when show ratings = ad money.

The pic shows Matt purchasing a pair of ski boots today at Surefoot in Vail, Colorado.

The salesman tells TMZ, Lauer came in and said, "Gimme the best thing you have for my foot" ... so he obliged.

Coincidentally, the salesman's friend is Matt's ski instructor ... who called Matt a "solid skier."

While Matt plays in the snow, the "Today" show is getting trounced by "Good Morning America" -- on Monday, "GMA" beat "Today" by 800,000 viewers. On Tuesday, nearly a million.

And today should be devastating for "Today" because it's Robin Roberts first day back on "GMA."