You can connect to any Matrix room hosted on any Matrix server via Bifrost Matrix bridge (which is hosted by Matrix.org). To join a Matrix room:
#room is the Matrix room you want to join and
matrix.domain.tld is the Matrix server address you want to join. Make sure to leave
@matrix.org as it is, because it's the Matrix bridge address.
As it is mentioned in the Bifrost's code page:
This bridge is in very active development currently and intended mainly for experimentation and evaluation purposes
So please keep in mind that this "bridge" is unstable and sometimes it can be down.