is it worth a visit in the winter. 3 days are planned so have open day on Saturday 12/6. Would like to do the Christmas markets and thinking about seeing the HighLine I have been hearing about. what can I expect to see and do...

You tagged both NM and NY. Are you talking about the Highline park in NYC or a highline somewhere in the southwest?

Highline depends very much on the weather since it's right next to the river. If you get bad weather it's not very pleasant.

If you do walk it, head north. If you walk south the sun will be in your eyes.

Yes, since it is free, it is worth visiting any time of year.

It's definitely worth seeing NYC in winter, and by early December the weather isn't that cold in most years (not sure about this year since it's been all over the place).

What you can do outside depends entirely on your stamina and feelings about the cold, but the Highline is open and always worthwhile. I'm less sold on our Christmas markets, though the one at Union Square is usually the best. I've heard mixed things already about Bryant Park this year. But if you like ice skating, there are opportunities all over town, including some that are free (though you have to pay to rent skates at Bryant Park). Just avoid Bryant Park on weekend nights. It's too rowdy.