Have visited Chiang Dao Caves several times. Taken several friends on this trip. Great setting with toilets and drinks/food and parking available all around. You pay a fee each to go in about 50 baht this gives you access to the area lit by electric light. Part way through you meet guides with paraffin lamps who will escort you through the extensive un-lit areas. You pay the guide seperatley to the entrance fee about 200 baht per group - they have only a little english.
My warnings are - if you have elderely or anyone who is unsteady on their legs - give it a miss. There is absoloutley no disabled access. The floor is slippery, muddy and wet. Health and Safety regulations are not applied here. I have had people fall in the caves and luckily although bruised where not hurt.
Take a bright torch to see the un-lit areas. Wear clothes that you don't mind getting muddy and sensible footware not flip flops. There is one very restricted area you have to crawl through so no claustrophobics! Steep concrete steps as well.
That said it's great fun and I would go again!
Visited February 2014