It's very easy to visit London from Guildford. Trains departing every 15-20 min each way make it an easy commute to plan. We decided we also wanted to visit Bath and/or Stonehenge but found out that it was a lengthy process: you either have to book an all day tour separately, take multiple trains (2+ hours one way) or rent a car.
We were talking with a friend about our desire to visit and coincidentally he had to go to a work presentation at Bath. He offered us an early ride there and a quick stop outside of Stonehenge to see the amazing site and take a few pictures.
So if you have an awesome friend who can drive you that is preferable otherwise plan in advance so you are hassle free. Many daily tours leaving from London will be your best option.
Even though we stopped at Stonehenge for a few pictures it felt quite amazing to be there and makes you want to read more and return! Crazy to know that it's been there's since 3000 BC.
On our ride towards Bath we saw many beautiful yellow flowers. These are canola flowers which makes great oil. Our friend kept calling them "rape" flowers and yes that's what they are called and have been known for many years! Canola is a varietal developed in Canada and known more recently (70s or so) by its new name in the US.
When arriving at Bath we were surprised to see such a nice and large city. To be honest we only knew about the Roman Baths and nothing else.
The city offers daily free tours and we were able to catch one. We learned more about it's influence in the Georgian era.
Free tour: http://visitbath.co.uk/travel--maps/explore-the-area/mayor-of-bath-honorary-guides-p43001
We spent the whole day walking around and exploring the highlights of the city: Roman Baths, Royal Crescent, The Circus, and Bath Abbey.
Walked around the narrow alleys and ate some amazing Cornish pastries at the Cornish Bakehouse.