Having made voyages through Italy (Apulia region), Greece, Turkey, and Asia Minor, he published: Studien über Wasserscheiden, Berlin, 1886; Der Peloponnes, ib.
Since 1887 Philippson undertook, on a commission from the Berlin Akademie der Wissenschaften, an annual journey to Asia Minor for the purpose of geological investigation.
His chief object in these excursions was to study, on a geological basis, the phenomena of the earth's surface both in their interrelationship and in their influence on the human race.
During the war, he was sent to the Theresienstadt concentration camp (1942–45), where he wrote a memoir on his scholarly activity (Wie ich zum Geographen wurde, partly published in 1996).
He survived the war in part thanks to the support of his friend, Sven Hedin, resuming work on his multi-volume essay on the Greek landscapes (with E. Kirsten; posthumously published and continued by Kirsten).