  Spin-nematic and spin-smectic phases have been reported in magnetic
materials, which break rotational symmetry while preserving translational
symmetry along certain directions. However, until now the analogy to liquid
crystals remained incomplete because no magnetic analog of cholesteric order
was known. Here we show that the bilayer perovskite Sr$_3$Fe$_2$O$_7$,
previously believed to adopt a simple single-$\mathbf{q}$ spin-helical order,
hosts two distinct types of multi-$\mathbf{q}$ spin textures and the first
"spin-cholesteric". Its ground state represents a novel multi-$\mathbf{q}$ spin
texture with unequally intense spin modulations at the two ordering vectors.
This is followed in temperature by the new "spin-cholesteric" phase with
spontaneously broken chiral symmetry, in which the translational symmetry is
broken only along one of the crystal directions while the weaker orthogonal
modulation melts, giving rise to intense short-range dynamical fluctuations.
Shortly before the transition to the paramagnetic state, vortex-crystal order
spanned by two equivalent $\mathbf{q}$ vectors emerges. The "spin-cholesteric"
phase completes the spin analogy with liquid crystals and renders
Sr$_3$Fe$_2$O$_7$ a touchstone for studying transitions among
multiple-$\mathbf{q}$ spin textures in a centrosymmetric host.
