admission free; free to attend
Used for public hearings, trials, lectures, or meetings that are open to the public without charge.
The city council plenary session is free for the public to observe.
This lecture is free to attend.
傍聴 means 'hearing' or 'observing' (a trial, meeting, etc.), while 傍聴無料 specifically means that such attendance is free.
無料 means 'free of charge' in general; 傍聴無料 is a specific compound for free admission to hearings or public sessions.
Compound of 傍聴 (hearing, observing) and 無料 (free of charge).