The opening of a planned visitor centre in Falkirk, Scotland, has been delayed for further expansion after visitor numbers to the Kelpies doubled original expectations.

Work on the development has already started nearby artist Andy Scott’s giant horse-head sculptures, which are at the centre of the Helix parkland project.

The sculptures debuted in April 2014, with more than 680,000 people visiting by September and an estimated 950,000 to visit in the first full year.

The £1.8m (US$2.9m, €2.4m) visitor centre – designed by Dundee-based architects Nicoll Russell Studios – will now open in October rather than August to allow expanded retail space, storage and additional staff facilities as well as the originally planned café, shop, toilets, offices and exhibition space.

Inside one of the sculptures is a 250sq m (2,690sq ft) visitor centre, while the “Hub” visitor centre is an environmentally focused green roofed building designed to blend into the landscape. A frameless glass facade is oriented directly toward the sculptures and the remaining facades and roof are constructed of Composite cross laminated timber panels.

Funding has been secured from Score Environment, the Scottish government, the Big Lottery Fund, Falkirk Council and Scottish Canals. Temporary visitor facilities will continue to be available on-site until the centre is ready to open.