Enable baked ambient occlusion (AO).
Ambient Occlusion (AO) approximates how much ambient lighting (lighting not coming from a specific direction) can hit a point on a surface. It darkens creases, holes and surfaces that are close to each other. Such areas block out or occlude ambient light, hence they appear darker. You can configure if AO should affect direct lighting, indirect lighting or both. The default is indirect lighting only. AO on direct lighting is not physically correct but can be used to achieve a specific art style.