Taking O(D, D) covariant field variables as its truly fundamental constituents, Double Field Theory can accommodate not only conventional supergravity but also non-Riemannian gravities that may be classified by two non-negative integers, (n,n). Such non-Riemannian backgrounds render a propagating string chiral and anti-chiral over n andn dimensions respectively. Examples include, but are not limited to, Newton-Cartan, Carroll, or Gomis-Ooguri. Here we analyze the variational principle with care for a generic (n,n) non-Riemannian sector. We recognize a nontrivial subtlety for nn = 0, which seems to suggest that the various non-Riemannian gravities should better be identified as different solution sectors of Double Field Theory rather than viewed as independent theories. Separate verification of our results as string worldsheet beta-functions may enlarge the scope of the string landscape far beyond Riemann. arXiv:1909.10711v1 [hep-th] 24 Sep 2019 1.1 Double Field Theory as the O(D, D) completion of General Relativity While the initial motivation of Double Field Theory was to reformulate supergravity in an O(D, D) manifest manner [2-7] ([58-60] for reviews), through subsequent further developments [61-64], DFT has evolved and can be now identified as Stringy Gravity, i.e. pure gravitational theory that string theory seems to predict foremost. 1 More specifically, DFT is the string theory based, O(D, D) completion of General Relativity: taking the O(D, D) symmetry of string theory as the first principle, this Stringy Gravity assumes the whole massless NS-NS sector of closed string as the fundamental gravitational multiplet and interacts with other superstring sectors (R-R [67-69], R-NS [70], and heterotic Yang-Mills [71-73]). Having said that, regardless of supersymmetry, it can also couple to various matter fields which may appear in lower dimensional effective field theories [70, 74, 75], just as General Relativity (GR) does so. In particular, supersymmetric extensions have been completed to the full (i.e. quartic) order in fermions for D = 10 case 1 At least formally let alone its phenomenological validity, c.f. [65, 66].