Callow made his first tour of Italy in 1840. He visited Venice during the summer and accounts from his journal reveal his instant love of the city:
'Being anxious to arrive at Venice we embarked in a gondola, traversing several miles over the lagoon, and arrived in the evening at the steps of the Hotel Europa, delighted with our first view of the Queen of the Adriatic. We stayed for ten days, seeing all the wonderful sights and making many sketches. We left Venice with great regret' (J. Reynolds, William Callow R.W.S., London, 1980, p.75).
Callow began to exhibit Venetian views at the Old Watercolour Society in the following year. In 1846 his spent his honeymoon in Venice and he made frequent trips thereafter.