There are several major attractions along the route of Ensign 21, not just in Brentwood. If you fancy a day out, why not consider one of these?:
Secret Nuclear Bunker. Take the 21 to Kelvedon Hatch, The Priors.
Epping Ongar Railway. Take the 21 to Ongar Station.
Find out all there is to do in Ongar here and here.
The 21 now only goes as far as Ongar. Change there to other buses to see the following:
North Weald Airfield Museum.
There are also things to discover in Epping (more here) and Harlow (more here), so what are you waiting for?
The 21 runs from opposite Brentwood Railway Station and at stops K and B on Brentwood High Street.
Opposite Brentwood Railway Station on Warley Road.
Brentwood High Street, stops A, B and C from right to left.
Two Brewers on High Street, Ongar. Buses to Brentwood on the right.
The timetable and a route map for the 21 can be found at Traveline.
If you need to use another bus to connect with the 21, then you could save money by asking for an Essex Saver ticket, which allows you to use almost all buses in Essex for a whole day for just £8.
Do bear in mind though that the 21 does not run on Saturdays, Sundays or bank holidays.
Click here to discover more Great British Bus Routes across the South East.