The Cape Solander whale watching platform, adjacent parking area and road access have been closed for four months just as the annual migration season starts.
The move will allow a new, larger viewing platform to be built.
The timing is curious given the spectacular site normally attracts more than 300,000 local, domestic and international visitors each year. Obviously, with COVID-19, the number would have been less this year.
A statement on the National Parks and Wildlife Service website says, in 2020, landscape architects Oculus were engaged to design "a new platform that meets the needs of the many thousands of whale watching visitors, will withstand the harsh corrosive environmental conditions and improve pedestrian access and safety.
"Construction is scheduled to commence in May 2021. The works will take approximately four months to complete.
"Cape Solander lookout, the adjacent parking, and a portion of Cape Solander Drive will be closed during this time. Vehicle access will be closed beyond Yena, but all walking tracks will remain open."
NPWS said parking areas and safety barriers would be improved and a new footpath from the parking area to the whale watching platform provided.
"The proposal will complement and promote the scenic values of the national park and is consistent with the National Heritage listing of the site," the statement said.
NPWS advised migrating whales could be seen from "lookouts along the entire coastline of Sydney".
An explanation of the timing is being sought from NPWS.