In December 2020 I purchased a house in Norway. I will not rent it out but use it as a cottage for my vacations in Norway. Should I declare this anywhere?

Yes, you’ll need to declare any foreign property you own when it comes to filing your tax return. It’s also important to know the rules for declaring foreign property on your tax return. The rules only apply to certain types of foreign property with a value in excess of $100,000. For example, You don’t need to declare your cottage as foreign property if it's valued at over $100,000. 

For more information on declaring foreign property, see the link below:

Declaring Foreign Property on Your Tax Return