In this work, we experimentally investigate guided polaritons utilizing only 2D van der Waals materials, with hexagonal boron nitride (hBN) as the waveguide layer and WS2 monolayer as the excitonic medium. We place the WS2  monolayer at the maximum of the waveguide mode electromagnetic field, therefore reaching optimal conditions for the strong coupling between the exciton resonance and waveguide mode. To excite and detect the non-radiating waveguide polariton modes, we use the back focal plane microscopy with a high-index solid immersion lens. Polaritons in such all-van-der-Waals structures observed in ambient conditions reveal new possibilities for studying fundamental aspects of light-matter interaction and provide strong advantages in terms of miniaturization and integrability of future photonic devices.