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The icosahedron-based bulk boron structures have extremely chemical and structural complexity, and are usually semiconductors at ambient conditions. Here we predict bulk boron phases with a 60-atom orthorhombic unit cell from an ab initio evolutionary structure search, termed as ${\mathrm{B}}_{60}$. The metastable structures can be either a conductor or a semimetal depending on their interstitial atomic positions. In particular, an orthorhombic structure with $Pnma$ symmetry ($Pnma\ensuremath{-}{\mathrm{B}}_{60}$), consisting of ${\mathrm{B}}_{12}$ icosahedra and twisted interstitial two-atom wide boron ribbons, is identified to be a topological node-line semimetal with potential superior electronic transport. The band structure and simulated electron-diffraction pattern of $Pnma\ensuremath{-}{\mathrm{B}}_{60}$ are in satisfactory agreement with the experimental data, suggesting that it may exist in the form of nanomaterials.