The mountain route from Bonar to Vegacervera (27 km) is a five-star day. The walk starts off-road and climbs through pretty countryside to La Mata de la Berbula, where there's a cafe. From La Mata to the viewpoint is only 6 km, but it's a steep 300 m ascent — the view from the top, spreading across valleys and mountain peaks, is spectacular and worth soaking in.
For shorter options: Ranedo de Curueno (8 km from Bonar) has Hotel Rural El Canto de Gallo. Valdepiélago (9 km) has several casas rurales. Or take a taxi to La Mata de la Berbula and walk the spectacular 12 km from there.
The flat route to La Robla (33 km) avoids the mountains. Shorter stops: La Vecilla (9.5 km, Hostal Las Hoces), Aviados (14 km, Albergue Fuente de Oso, tel. +34 666 605 835 — reserve in advance), Robles de la Valcueva (20 km, Hotel Rural el Arriero), Candanedo de Fenar (25 km, Hostal el Valle).