Work underway prior to filming in Norway in March and April according to local media reports.

Back in January we reported how a Norwegian company, Truenorth Norway, had been awarded a grant of nearly €5 million by the Norwegian Film Institute for production services on Bond 25. At the time the announcement only said that producers were considering using Norway for filming.
With such a large sum of money changing hands it always seemed likely that Norway would be used. The country was previously considered for SPECTRE but lost out to Austria.
A few days ago reports surfaced that a house was being constructed for Bond 25 in Hakadal, which lies in the municipality of Nittedal. Those reports now appear to have been confirmed after a local website saw a filming application submitted on behalf of B25 Limited (via The Spy Command).
According to the latest reports filming will take place in Nittedal between 25th and 31st March 2019. Furthermore, filming is also due to take place at lake Langvann for a week in March/April.
The report contains a spoiler, which you can click to reveal below.
Possible spoiler: click here to reveal
The article says the documents submitted include the following information about the scene:
This sounds like a flashback to Madeleine Swann’s childhood, an incident alluded to in SPECTRE.