Dudley Zoo in the West Midlands, England is set to invest £6m (US$7.7M, €6.8m) in an expansion which will include utilising a network of wartime tunnels underneath the zoo.

Zoo bosses have drawn up plans that would make the attraction "more than a zoo" as visitors would be able to go explore an underground limestone cavern, seeing the mining history of the area.

Other details in the plans include the zoo’s 1930s buildings being revamped, as well as a new education centre being built and the zoo entrance being refurbished.

The number of visitors to Dudley Zoo has doubled in the past 10 years and is now at 300,000 per year. This increase in uptake, according to zoo director Derek Grove, has allowed zoo chiefs to think about investment.

"We want to build a training and education centre. We probably get 20,000 children in a year and we want to grow that," said Grove.

"There’s an area between the car park and the zoo and we’re looking at opening that up.

"There is also a cavern and we want to take people down. We’re planning to go into the history of the mines."

The zoo will put some of its own cash into the expansion, while other funding streams, such as the Heritage Lottery Fund, will also be pursued.

Work on the expansion is expected to begin in 2020, if plans are accepted, while no projected opening date has as yet been made public.