  We probe a slice of the massive winding sector of bosonic string theory from
toroidal compactifications of Double Field Theory (DFT). This string subsector
corresponds to states containing one left and one right moving oscillators. We
perform a generalized Kaluza Klein compactification of DFT on generic
$2n$-dimensional toroidal constant backgrounds and show that, up to third order
in fluctuations, the theory coincides with the corresponding effective theory
of the bosonic string compactified on $n$-dimensional toroidal constant
backgrounds, obtained from three-point amplitudes. The comparison between both
theories is facilitated by noticing that generalized diffeomorphisms in DFT
allow to fix generalized harmonic gauge conditions that help in identifying the
physical degrees of freedom. These conditions manifest as conformal anomaly
cancellation requirements on the string theory side. The explicit expression
for the gauge invariant effective action containing the physical massless
sector (gravity+antisymmetric+gauge+ scalar fields) coupled to towers of
generalized Kaluza Klein massive states (corresponding to compact momentum and
winding modes) is found. The action acquires a very compact form when written
in terms of fields carrying $O(n,n)$ indices, and is explicitly T-duality
invariant. The global algebra associated to the generalized Kaluza Klein
compactification is discussed.
