Wat Ban Den is a huge temple that keeps getting bigger. Architecturally speaking, you will find a lot of different elements and styles with an amazing sense of detail. It is a beautiful place but I must admit that I did not find in it the little extra soul that I usually feel in temples in Thailand. I have been there twice and had this feeling of the place being a little artificial both times. But it is probably just me and whatewer it's still an interesting visit and a stop that I recommend on the road from Chiang Mai to Chiang Dao.
To get to the temple, there is no local bus line, you have to your on transportation or privatize a red car to take you there, wait for you when you visit and bring you back in Chiang Mai.
Note that each year for Loy Krathong and Yee Peng Festival in Chiang Mai (usually in November, the date varies each year as it is based on the lunar calendar), a big release of sky lantern is organized in the temple. But you have to pay to attend it and the ticket is quite expensive (around 100 euros per person).