You've played CS:GO's maps. Now see how the poor mappers made them. Get Hammer++ here: https://ficool2.github.io/HammerPlusPlus-Website/
0:00 - Hammer++
1:04 - Real-time lighting
3:10 - Fog
3:38 - Skyboxes
4:45 - Rope physics
5:19 - Particles
6:40 - Placing things in your level
7:13 - Sprinkling lots of props
8:00 - Putting props on the ground
8:22 - Physics tool!
9:25 - Hammer can't count
10:00 - Other
10:16 - Conclusion