Before you dive into the tunnel, a word of caution. "Escaping prison unblocked" is a game genre—not an instruction manual for real life. However, circumventing school or work firewalls exists in a legal gray area.
If you search for "escaping prison unblocked," you aren't looking for a single game but a genre. Here are the top 5 titles currently dominating the unblocked gaming circuit.
Some savvy developers upload "escaping prison" game files as .html files to their personal Google Drive. Because Drive is a whitelisted domain (schools cannot block Google Drive), you can play the game directly in the browser. Search for: site:drive.google.com "escaping prison".