The www.vtk.org DNS record points to web.kitware.com using a CNAME, but web.kitware.com is not known.
Various links on the VTK homepage (on https://vtk.org, not www.vtk.org) point to www.vtk.org, and lead to nowhere.
Same issue with wheels.vtk.org. I work with a project which is installing one of the osmesa releases from there and so we are unable to deploy at the moment.
Sorry, folks. We had an issue with our DNS records today. A fix is underway and these resources should be back shortly.