Allen had continued to design houses and other buildings during the war years; he was the designer, for instance, of the noted Trenton House, Oneida, for J.A.H Burnett and of St Stephen's Church in Marton. By 1869, however, he was able to return to surveying. He surveyed in the Waitotara Valley and on the Whanganui River. His work on the upper Whanganui River took him into the mountains and he climbed Ruapehu, Tongariro and Ngauruhoe, revelling in the grandeur of the area. He was an accomplished watercolourist, like many other surveyors, such as Whanganui man John Tiffin Stewart. When finding themselves at a loose end at the end of a long day's work in the bush or the high country, they would sit down and sketch.
Allen built a summer camp and coaching stop between Waiouru and Taupo on the Waihohonu Stream. From there, he took guided tours into his beloved mountains. His writings were published in 1894 in Willis' Guide Book of New Routes for Tourists, promoting the trip from Auckland to Whanganui through the mountains and down the Whanganui River.
In the 1890s he also painted the mountains in a series of literal, measured, panoramic watercolours, all precisely annotated as to time, date, distance and landscape identification. These were donated to the Wanganui Public Museum in 1930.
Libby Sharpe is senior curator at Whanganui Regional Museum