National Trust for Scotland will spend £57m (US$76.1m, £65m) on the country's built and natural heritage, the largest and most ambitious programme for investment the charity has ever proposed.

To be spent over the course of the next five years, the Trust's plan is a framework that commits to modernising its approach. As part of this, the body will invest in technology, also developing learning experiences for more than 100,000 people each year.

It will also introduce new, engaging and more inclusive ways to present its collections, gardens and Scotland's history.

The framework aims to increase visitor numbers to more than five million people, increasing annual donations to more than £10m (US$13.3m, €11m) and its membership to 490,000 people.

"This strategy outlines everything that the National Trust for Scotland stands for: protecting our heritage, sharing unique experiences with people and promoting Scotland, all through the collective endeavour of our supporters and staff," said Simon Skinner, National Trust for Scotland, chief executive.

"To do that, we need to create an efficient and sustainable business which delivers our conservation ambitions.

"This plan for the next five years sets out how we can make the Trust fit for the future."

Priority projects for the trust during the five-year period include the £1.5m (US$2m, €1.7m) "box construction" of Charles Rennie Mackintosh’s The Hill House in Helensburgh. The ambitious plans will see a structure built around the iconic property to protect its sandstone structure, which is dissolving through elements such as rain.

The Trust is implementing its new strategy on the back of a reorganisation last year. As part of that reshuffle, it created six new regions and a division responsible for natural heritage to oversee work on its portfolio.