Can you recommend a Linux program that allows me to visualize CityGML models (3D)?
I have tried a whole bunch so far (most of them via wine but also native ones) but I couldn't get a single one of them running.
I am using Ubuntu 13.04.
Aristoteles 3D (requires Java) is working on current versions of Ubuntu.
From memory, the link I used was from https://www.citygmlwiki.org/index.php/Freeware, pointing to http://www.geo-kiosk.net/explore-3dgeo/ (no longer working)
Current working link (not tested, this was uploaded more than 10 years ago): https://sourceforge.net/projects/aristoteles3d/
If you have a lot of such files, it might be easier to just bulk convert CityGML into another format that is more suitable for viewing (one of those 3d formats like OBJ etc)
3DCityDB supports CityGML: https://www.3dcitydb.org/3dcitydb/
At first you need to import a CityGML file to the database (I would suggest PostGIS) and then you have 3DCityDB-Web-Map-Client based on Cesium JS which allows to visualize all the features.
Just to add there is a data warehouse tool FME. It's a set of tools, very easy to use, also have extensive customer support since it's a commercial software. You can use it for free if you are a student.