许多罪犯被关押在阿尔卡特拉斯监狱，因为它被认为是无法逃脱的。

Many criminals were sent to ___Alcatraz because it was considered escape-proof.

许多游客乘船去参观著名的恶魔岛监狱遗址。

Many visitors take a boat to see the famous ___Alcatraz prison ruins.