It's the grave of a couple, who as the first line says "saw and loved the beautiful wide world".
He was born in Braunschweig (Brunswick) in the (back then) Duchy of Brunswick in 1883.
His wife was born in Esslingen in 1886, back then part of the Kingdom of Württemberg.
How they met, we do not know, but they must have travelled the world together.
He died in New York in '42, and she died in Phoenix in '50.
Now they rest together here in her native city of Esslingen, Germany.