Last month we had a week long vacation to Sardinia. You can watch the vlog here. I managed to stay keto the entire vacation, without too much effort. It was quite easy to stay keto actually. I did give myself a talking to before we came and I decided that I was going to do a totally keto vacation to show you guy that it absolutely can be done. I thought that I was going to fail at the first hurdle when we got to the lounge in the airport. It was all carbs.
As for key events in December, I typically avoid those sorts of things myself, so I’m not a good source on that. I actually visited Rio de Janeiro during Carnival, by accident, and it drives hotel prices so high and also crowds that it’s probably the worst time to visit unless you specifically want to spend all night watching the parades. And Oktoberfest, as another example, literally triples the prices of hotel rooms in Munich, so it’s only worth it if you REALLY want to get involved in the Oktoberfest thing yourself. But plenty of other travelers love to go witness the biggest events, and I assume they love it, so there is no right or wrong.
Needless to say, Australia is a huge country so you could spend 6 months there and not get bored, or you could spend one week there and barely see any of it. The obvious destinations are Sydney and Melbourne, both with plenty to do for non-beach people. Melbourne is known a bit more for culture and food, while Sydney is more pleasant and still very interesting. There is also the Great Ocean Road, which is a very scenic drive just a bit south of Melbourne.
You mention New Zealand and of course it’s summer there then, so it would be a good choice. However, all of these places will be crowded and near peak hotel rates if they are warm. So I’ll be happy to give you advice if you tell me if you’d rather visit one or more European cities in the cold season, or if you are looking for a warm place like New Zealand where it will be fairly crowded. By the way, the southern European cities such as Rome and Barcelona are lively and enjoyable that time of year, as the Christmas season goes on, and there aren’t too many tourists except for a few that travel to see their families around the holidays. So it can be a good time for southern Europe, as long as you don’t mind wearing a jacket or jumper during the day, and maybe a bit more in the evening. Give me a bit more guidance and I’ll be happy to try to help. -Roger
By early December the rainy season is pretty much over in Cartagena, and it cools down just a bit more as well, so the weather really doesn't get any better than this. As with most others on this list, right around Christmas you'll find that hotels get more expensive and are more crowded, so if you can go earlier in the month you'll be paying less and dealing with fewer crowds.
Since flights to Mexico City from the US and Canada are usually quite cheap this time of year as well, this could be a perfect short cultural holiday. This city has great shopping, dining, and nightlife, and the central historic and tourist districts are far safer than most people would expect. There are ruins just out of town as well, so a bit of everything is available.