Through the kissing gate, cross the road, and take the byway opposite. The byway is in very good condition, and should be drivable easily.
There's more details about this series (including parking) on the Chiltern Hundred web site.
You're looking for a 330 ml screw-top beaker. Remember to collect the letter value in the log.
Gur penfu oneevre jvyy raq nal penfurf.