Throughout the trip he mailed postcards to his eight year old daughter Paulina, who was in Vienna at the time.
The National Library of Israel has recently digitized a collection of these postcards; they can now be viewed online here.
The messages on the postcards contain short but heartfelt expressions of love for his daughter.
On one dated October 15, 1898, Herzl wrote "Tender kisses to my delicate daughter Paulina from her faithful Papa." That particular postcard was sent from Constantinople, which would soon be renamed Istanbul.
"Herzl is remarkable in that his greatness has almost universally been recognized across the Zionist spectrum," commented Dr. Hezi Amiur, curator of the National Library's Israel Collection. "There are few if any other figures in Zionist or Israeli history for which this can be said."
The postcards are from the Abraham Schwadron Collection at the National Library.