Serious Sam 4

In the mission "Breakfast in France" get to the motorcyles, hop on one, then do a 180 and follow the road until you eventually see a road on your right with a blue path leading to a side mission. Once there follow that road until the mission pops up and follow the objective markers until you complete this side mission and your 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.

At the start of "Breakfast in France" you'll run down the hill to a few houses with a motorcycle, jump on the bike and spin around 180 degrees. Follow this road driving away from the main objective for roughly one minute until you reach a dirt road bearing right. As you approach it will show the side quest and blue chevrons, follow this second road to the very end to find a hanger and a box to interact with. Upon opening the box the "Mushroom Surprise" achievement will pop.