Eldborg is the name of a wonderful evenly formed crater located on the Snæfellsnes peninsula in Iceland.
Eldborg can be literally translated with the term fire castle.

In Wikipedia you can find the following:
The crater Eldborg í Hnappadal (also: Eldborg á Mýrum ) is a lava ring and is considered to be one of the most beautiful in Iceland . It is located about 40 km north of Borgarnes and west of road No 50, which leads to the Snæfellsnes. The main crater measures about 200 meters in diameter, is 50 m deep and has inside and outside very steep walls. The last eruption took place about 5000 years ago and created the Eldborgarhraun lava field. Three smaller craters are located in the neighbourhood ...
There is only little to add. The short hike to the crater and the walk upon it are highly recommendable. I found the uniformity with which nature has created this fire castle fascinating from the beginning.
So the choice of my internet domain felt right after the first trip to the crater spontaneously on the name Eldborg. On the same evening I registered the domain www.eldborg.de from our summer house.