This is a type of Norwegian embroidery, popular also in the northern midwest USA. It’s very geometric with lots of square eyelets and lacy fillings. Nordic Needle’s specialty is hardanger, and they provide an extensive overview of the topic, lots of designs for sale, and some free patterns. What’s more, there is a full series of free lessons: 101, 201, 301, 401, and Weaving.
Now that we are all experts in hardanger, I am declaring the following two designs the coolest hardanger I can find on the internet. If you find something even better, I’d really love to hear about it.
Offbeat Hardanger: I have the instructions for this one, designed by Jonalene T. Gutwein at Friends in Needlework, and I am definitely going to make it (or maybe a portion of it since I’m super busy – it really divides up well. Even a quarter of it would look good).
Carol Pedersen has designs available through Nordic Needle, like Birdsong, a musical design that is rather larger than I want to attempt (but maybe I could just do a few notes from it!).