HEIÐMÖRK: EASY ACCESS TO FUN EASY TRAILS IN A NATURE RESERVE. The nature reserve consists of lava formations and bushy vegetation. Heiðmörk is the principal outdoor recreational area of Reykjavík. The 10-40 km of man-made semi gradual gravel trails are great for beginners and families, as well as being an overall fun cross country experience. It is a popular recreational area in Iceland. Rauðhólar are a notable natural formation of Heiðmörk, a cluster of red coloured pseudocraters.