R.V. Anderson Associates Limited (RVA) is working with Noventa Energy Partners (Noventa) and Bird Construction (Bird) on the Toronto Western Hospital (TWH) Wastewater Energy Transfer (WET) Project. Once complete, it is believed that it will be the world’s largest operating WET system. Over the next 30 years, the project’s goals are to supply 1.8 billion kilowatt-hours of energy to heat and cool TWH. The project site is located adjacent to TWH at the intersection of Dundas Street and Bathurst Street in Toronto, Ontario. RVA is responsible for the design of two major structures on the project: the Energy Transfer Station (ETS) Building and the Wet Well (WW) shaft. The ETS is a multi-storey structural steel building constructed inside the shell of an existing pre-cast concrete and masonry building (formerly a bank). A significant underpinning operation of the existing building was completed to create the additional space required to accommodate the heavy process/mechanical equipment and piping. RVA designed the new internal structure to resist temporary loads from construction sequencing, permanent loads from the existing building and proposed equipment, and future loads from the upcoming phases of the project. The WW shaft is a cast-in-place reinforced concrete structure 9.5 m in diameter and 39 m below grade within both overburden soil and shale bedrock. The shaft is used to capture and return raw sewer flows from the City of Toronto’s existing Mid-Toronto Interceptor Sewer via two (2) new diversion and return tunnel connections deep within the rock. RVA designed the WW to accommodate process mechanical equipment (ex. screens, pumps, and valves), and operations infrastructure including two PVC vortex drop structures, substantial piping, maintenance platforms, and internal concrete wingwall and chamber structures. This paper summarizes various components of the structural design for the ETS building and WW shaft. A primary focus is on design challenges and the unique solutions that were used.