Take the ladder up the scaffoldiing and you should find another two up here 4 5. Keep moving forward until you reach the level that pulls the rock towards you. Continue further along, jump down to the rock where the first ramp you need to lower is located. Start by running up the ramp and around to the left the usual path and you will encounter your first protozoan 1 right near a dead scientist. You must kill all 64 protozoans the purple glowy bois in the 3 new chapters. Prolific popper is a new achievement which came with the 1.
Black Mesa - How to Obtain The Rarest Specimen Achievement (Xen Chapters Tips)
