Serious Sam 4

Go to the level The Die Is Cast and continue with the main quest Head Into Rome. When you getting downhill and looking on main objective marker and you see 350 m distance. Then on right side you can find starter for side quest Portal Kombat. Then just follow white marker and finish an easy side quest, where you need to activate 5 buttons and kill some enemies.

For this achievement you will find a side mission called "Portal Kombat" on the mission "The die is cast" when you are making your way into rome. Follow the path and continue defending the portal until all 5 buttons are pressed and the achievement will pop. To make this easier make sure you have infinite ammo turned on and even tourism difficulty or play on co-op and set respawn timer to 0.