In 1879 Zöller started his travels around the world. The result was a two volume book Rund um die Erde (Köln 1881). In 1881 and 1882 he travelled across South America and then published Die Deutschen im brasilianischen Urwald (Stuttgart 1883) and Pampas und Anden (Stuttgart 1884).
By the end of 1882 he worked as a war correspondent in Egypt during the British campaign there. In 1883 he was ordered to explore territories in Western Africa previously explored by Gustav Nachtigal. First he travelled across the Togoland, then he went to Cameroon where he in 1884 made a successful ascent of Mount Cameroon together with Stefan Szolc-Rogoziński.
In 1888 he travelled to German New Guinea and became the first European to penetrate into inner New Guinea and climb the peaks of Finisterre Range. During this he also discovered Mount Wilhelm in the Bismarck Range.