GM Tip: 60-feet in Darkvision (or Lowlight-vision that doubles the radius of a 30-ft torch) may seem like a lot, until you realize your player characters exist in 3D space. A hall or cave with a 60-foot ceiling means the PCs can only see the ceiling directly above them.
And that's without cover, the possibility of hidden monsters increase dramatically with line-of-sight blockers such as statues, stalactites, chandeliers, mist/fog, magic curtains of darkness, etc;