The Maps of Opposing Force: Crossfire
Channel: Newline Void
Date: 2022-09-15

I'd imagine more people would be playing this game online if this was included by default.

Just a hunch.

You can download this map here:
https://www.moddb.com/addons/valves-official-hldmop4dm-pc-content

See this map in Half-Life:
https://www.youtube.com/watch?v=N6UwYCbosWY

See this map in Team Fortress Classic:
https://www.youtube.com/watch?v=BnbRrB4qejA

Series playlist:
https://youtube.com/playlist?list=PLqisjDcUjrDoIu226Zur3UHJHiSmAUgHi