I was into making Half-Life maps on pc in the early 2000's. One of my most popular maps was called "Eds Grocery Store". I used to work at a grocery store when I was a teenager, so that inspired me to make a deathmatch arena out of one. There are long shopping aisles and quite a few Easter eggs that I placed throughout the map. I told one of the secrets to my nephew about how you can flood the map and drown everyone and he got kicked off of a server because they thought he was hacking. I guess that secret was kinda hard to find. You have to climb into the ceiling, smash one of the walls, and you will find the button to let the chaos begin. You can see it in action in the video:
I came up with weird concepts for levels. Some of them worked and some of them didn't. I'll let you be the judge if you want to take them for a test drive. Just unzip them in your \Half-Life\valve\maps\folder and you should be good to go. Do people even play Half-Life anymore? Let me know what you think!
The pc I used to create these maps had these specs:
AMD TBIRD 1.0 Ghz, 512 MB DDR RAM, Nvidia Geforce 2 gts 64MB