Access to digital maps and geospatial information has become an integral part of modern applications to support mobility. However, for people with visual and mobility impairment, provided digital solutions are insufficient, target only one of the mentioned user groups, or are exclusively developed for outdoor environments. Research on accessible web-based indoor maps for people with impairments is still sparse. This paper presents the concept and prototype of an accessible web application that provides indoor map data and information on accessibility features of buildings to users with visual impairment, blindness, mobility impairment, and users without impairments. Results of a user study with 24 participants from all target groups show good to excellent usability (mean SUS score: 80), with room for improvement for users with severe visual impairment and blindness (mean SUS score: 66.7).