It is indeed on the lowest pulley - it is lower down than in your picture. If you kneel down at the front of the car and look under you'll see it. Like said previously, the nut is 27mm. You'll need a socket with a stubby extension to reach it whilst allowing you to attach a ratchet without fouling the radiator.

I found a 27mm deep impact that fits perfectly between the nut and my 1/2" ratchet

EDIT:- found a picture for you...

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!