Section 38. The commissioner may lay out, construct and maintain trails or paths through or over lands in state forests and in public reservations and trails or paths leading to important mountains and other objects and places of special interest and beauty and he may connect such trails or paths in order to make them continuous so far as practicable. The commissioner on behalf of the commonwealth may purchase such lands or easements therein as may be necessary for the aforesaid purposes. He may post such trails or paths, erect signs thereon and construct suitable rest camps or shelters at appropriate places. He may by special permit in writing allow portions of such trails or paths to be enclosed and used by the owner of adjoining land, for any use not interfering with public passage on foot, during the whole or any part of the year upon such conditions as the commissioner may prescribe and such permits may be revoked at his pleasure. The commonwealth shall not be liable for injury or damage sustained on such trails or paths.