This study reports the discovery of wandering principal optical axes in van der Waals triclinic materials, specifically rhenium disulfide (ReS₂) and rhenium diselenide (ReSe₂). These materials exhibit a low-symmetry triclinic crystal structure, leading to principal optical axes that rotate with wavelength, resulting in wavelength-switchable propagation directions of waveguide modes. The physical origin of this phenomenon is explained using a multi-exciton model and ab initio calculations. The wandering principal optical axes enable new anisotropic optical phenomena and nanophotonic applications. The study demonstrates that the principal optical axes of ReS₂ and ReSe₂ rotate with wavelength, with rotations exceeding 110 degrees across the spectral range. This behavior is attributed to the non-orthogonal exciton resonances in these materials. The rotation of principal optical axes was experimentally observed using near-field nanoimaging, revealing the wavelength sensitivity of light-matter interactions in these materials. The results show that the principal optical axes vary rapidly at fundamental exciton frequencies and exhibit complex behavior for high-energy photons due to the rich excitonic structure of the materials. First-principle calculations of the dielectric tensors of ReS₂ and ReSe₂ confirm the experimental findings, showing that the principal optical axes vary with wavelength. The unique dielectric tensors of these materials provide great flexibility in optical engineering, enabling new phenomena such as negative refraction and the super-prism effect. The study highlights the potential of triclinic van der Waals materials for advanced nanophotonic applications, offering a platform for exploring unexplored anisotropic phenomena. The findings suggest that other low-symmetry crystals with triclinic and monoclinic structures may also exhibit similar properties, opening new avenues for wavelength-switchable metamaterials and photonic devices.This study reports the discovery of wandering principal optical axes in van der Waals triclinic materials, specifically rhenium disulfide (ReS₂) and rhenium diselenide (ReSe₂). These materials exhibit a low-symmetry triclinic crystal structure, leading to principal optical axes that rotate with wavelength, resulting in wavelength-switchable propagation directions of waveguide modes. The physical origin of this phenomenon is explained using a multi-exciton model and ab initio calculations. The wandering principal optical axes enable new anisotropic optical phenomena and nanophotonic applications. The study demonstrates that the principal optical axes of ReS₂ and ReSe₂ rotate with wavelength, with rotations exceeding 110 degrees across the spectral range. This behavior is attributed to the non-orthogonal exciton resonances in these materials. The rotation of principal optical axes was experimentally observed using near-field nanoimaging, revealing the wavelength sensitivity of light-matter interactions in these materials. The results show that the principal optical axes vary rapidly at fundamental exciton frequencies and exhibit complex behavior for high-energy photons due to the rich excitonic structure of the materials. First-principle calculations of the dielectric tensors of ReS₂ and ReSe₂ confirm the experimental findings, showing that the principal optical axes vary with wavelength. The unique dielectric tensors of these materials provide great flexibility in optical engineering, enabling new phenomena such as negative refraction and the super-prism effect. The study highlights the potential of triclinic van der Waals materials for advanced nanophotonic applications, offering a platform for exploring unexplored anisotropic phenomena. The findings suggest that other low-symmetry crystals with triclinic and monoclinic structures may also exhibit similar properties, opening new avenues for wavelength-switchable metamaterials and photonic devices.