Here is a list of some free activities in Bangkok:

Visiting Wat / Temple
There are so many Wat or temples in Bangkok you can visit without paying the expensive entrance fee. Many of these free temples are as beautiful as that required admission. If you spend time at the Wat, you will also get a chance to see how the religious people of Thailand for their spiritual beliefs.

Window Shoppig

Looking around at the mall or a 'window shopping' is a popular activity for locals and tourists who want to spend a hot afternoon in an air-conditioned building. Visiting the mall is also a great way to observe local life, especially the young people of Thailand. Siam Square is the perfect place to also see the work of young Thai designers.

Visit the Traditional Market
Visiting the market in Bangkok is one of the favorite things that I often do whenever, or wherever I travel. Certainly free to market (unless you buy the goods) and it helped me learn a lot by watching the locals as well as the products sold. There are so many things that you will see in the local markets of Bangkok that you might not find in your home country.

Visit to a butterfly garden and InsectariumA short walk from the Chatuchak weekend market takes you to a park, houses a variety of butterflies and insects. There are hundreds of butterflies here and display the information board that will help us understand and learn more about these beautiful creatures.

Tasting food
Go to the supermarket, take a walk and do the taste test or take samples of food from several local food is sold. Small portion was prepared for buyers who want to try.

Viewing wildlife
In addition to cats, dogs, and rats are commonly found in many cities, you will be surprised to find some other animals around Bangkok. There are lizards that are often seen in Lumphini Park, squirrels, crows and various other birds. Afternoon is the best time to see the squirrels running around looking for food in the local park.

Visit the Museum
A number of free museum entrance fee, some peg the price of admission is very cheap and worth a visit. Some include: Royal Elephant Museum, Museum and Museum Bangkokian Correction.