There is a loveley AC Festival in Devon every year sometime in september: http://www.agathachristiefestival.com/
And you can explore the english reviera for AC http://www.englishriviera.co.uk/agathachristie
Her summer house Greenway is partly featured in Dead man`s Folly - it is a very beautiful place and you get some insight into her love for gardening and interior decoration with foreign art and craft.
There is also a interesting guided walk through Torquay where she lived a long time in her youth.

If you are interested in her way of creating a plot you might like to see one of John Currans`s books (murder in the making, secret notebooks) - he had access to over 70 of her writing journals and tried to bring some structure into them - it makes more sense to read his books if you now most of ACs novels as he has to reveal al lot of the twists and murderers to show her creating process.