Currently, there are only streets and lawns you can see in the visualization. Accrodingly there is nothing in the simulated environment but a street graph and vehicles.
Please extend the environment builder so that it extracts buildings , waters, etc. from the OSM provided and instantiate corresponding objects in the simulation. Make sure these objects have an influence on driving, e.g. a vehicle cannot drive through a building.
In a second step it is necessary to extend the visualization so that buildings and waters are rendered as such in the 3D visualization.