Police in Inverness are appealing for witnesses following a fire at Boleskine House near Foyers.
The incident was reported around 3.30pm on Wednesday, July 31.
Fires were reported at two buildings on the site, including the derelict main house and at an external outbuilding.
The fires were extinguished by the Scottish Fire and Rescue Service.
Nobody was injured, although damage was caused to the buildings.
Detective Inspector Eddie Ross said: "We are working with the Scottish Fire and Rescue Service to establish the full circumstances.
"Our enquiries are at an early stage, although our initial assessment is that this fire was started deliberately.
"We would encourage anybody may have seen any activity around Boleskine House or nearby to come forward as soon as they can.
"It should go without saying that deliberately setting fires is incredibly dangerous as you have limited control over how they may develop.
"Anyone with information about this fire can contact Police Scotland on 101, quoting incident 3619 of July 31, or call Crimestoppers anonymously on 0800 555 111."