Excerpt from
www.historicplaces.ca:
The gatehouse or folly was constructed in 1904 as a summer nursery, doubling as a guesthouse. It is one of only three gatehouses of this design in Canada. (The others are at the Ottawa residences of both the Governor General and the Prime Minister.) It is also Canada's only wooden folly. Thus, this structure is valued for being an architectural rarity. It spans the driveway that leads to the rear of the main structure. The green roof shingles and wood trim stand out against the cream-coloured stucco and complement the exterior colours of the house. An exterior staircase accesses the upper floor and leads to a wrap-around balcony.