Complex sentence: The French also came at night to sign the peace treaty between France and Spain in which Spain was represented by Domingo d'Yriarte, who signed the treaty in the mansion of Peter Ochs, the Holsteinerhof.
Split into simpler sentences: The French also came at night to sign the peace treaty between France and Spain, where Spain was represented by Domingo d'Yriarte. This time it was done in the mansion of Peter Ochs, the Holsteinerhof.