A World War II pillbox will become a home for bats if Cambridgeshire volunteers get their way.
Volunteer group Ely Wildspace wants to develop the derelict building at Ely Common, a Site of Special Scientific Interest (SSSI).
The group's chairman, Liz Hunter, says there are bats in the area and the box is a potential habitat for them.
"We're quite sure that given time, when they get used to this, they will eventually take up home," she said.
The group has taken advice from the Bat Conservation Trust, and the conversion will include building steel doors to block access to the pillbox for all but bats.
Ms Hunter said: "Inside we'll use bricks to build structures with spaces between so bats can roost.
"We'll also use bricks called frog bricks, which make a very good small space for the bats to spend the winter."
Ely Common is part of an area of lakes, reed beds, woodlands and grasslands to the east of Ely.
Most of it has been granted SSSI status by Natural England.
The volunteers hope to start the work of converting the pillbox this spring.