Karla's Martensen ancestors were born in the small towns of Almdorf, Bredstedt, and Goldelund in Nordfriesland (in English, North Frisia), which today is the northwest region of the German province of Schleswig-Holstein. The coat of arms in the flag of the old district of Nordfriesland (with its motto "Better Dead than Slave") is shown at the top of this page and a map of its location in the modern province of Schleswig-Holstein is shown below.
Before 1864 Schleswig and Holstein were duchies of Denmark. In that year they were taken from Denmark by Prussia and the Austrian Empire in the Second War of Schleswig. In the following Austro-Prussian War (1866) they were annexed by Prussia when it defeated Austria; Prussia made them into a single province in 1868. After Germany was defeated in World War I the Allies organized plebiscites in north and central Schlewwig-Holstein to allow the residents of each region to decide whether to become part of Denmark or to remain with Germany. The northern region voted to reunite with Denmark and the central region voted to stay with Germany. Nordfriesland is the northwestern part of the region that voted to remain with Germany.
Goldelund is the farthest north of the three towns, lying less than 30 km (18 miles) from the present border between Germany and Denmark. Bredstedt is 12.5 km (7.8 miles) southwest of Goldelund, near the North Sea coast, and Almdorf is 7.6 km (4.7 miles) southeast of Bredstedt.
The photo below is labeled "Stammhaus Martensen in Almdorf" ("Martensen Ancestral Home in Almdorf") on the first page of the Martensen Genealogy.
Since the Genealogy starts with Jens Martensen, who lived from 1800 to 1861, I'm guessing that this is his home and that the unlabeled photo below is of him and his wife Anna Dorothea.