We present a procedural technique for the controllable synthesis of detailed terrains. We generate terrains based on a sparse curve network representation, where interconnected curves are distributed in the plane and can be procedurally assigned height. We employ path planning to procedurally generate irregular curves around user-designated peaks. Optionally, the user can specify base signals for the curves. Then we assign height to the curves using random walks with controlled probability distributions, a process which can produce signals with a variety of shapes. The curve network partitions space into individual patches. We interpolate patch heights using mean value coordinates, after which we have a complete terrain heightfield. Our algorithm enables user to obtain prominent features with lightweight interaction. Increasing the density of curves and roughness of curve profiles adds detail to the synthetic terrains. The curves in a network are organized into a hierarchy, where the major curves are created first and the curves constructed at later stages are affected by earlier curves. Our approach is capable of producing a variety of landscapes with prominent ridges and distinct shapes.