Bangkok is quite the city with a mix of old and new. On the one hand it is a metropolis with fancy clubs, Western amenities, and seriously impressive malls with high end shopping. You can order pizza from a Thai guy with a New York accent and attitude, eat at an "authentic Mexican cantina" (though I'm sure they've got nothing on Houston tacos), and get an amazing 1 hour foot massage for $3.
In contrast there are street markets like you wouldn't believe, homemade "vehicles" roaming the streets, questionable sanitary standards at times, no apparent rules of the road, so many stray dogs and cats, and bare bone dwellings stitched together with whatever can be found. Some of my best spent time in Bangkok was wandering to nowhere in particular, just taking it all in.
The temples are incredible and worth seeing. Intricate designs, giant Buddha statues with toes taller than me, great views, monks that will bless you, and SO much gold.
But a couple highlights have been off the tourist trail:
First, a local expat tipped me off to a park outside the city where I could escape the craziness of Bangkok and get my nature fix. From the last metro stop I walked out of a business district towards the port, where signs quickly lost their English translations. Through alley markets where locals do their shopping for the day: live ducks, buckets of frogs still hopping, and trays of fish-one flopped out onto the sidewalk in front of me. At the port I must've looked out of place, as a local asked, "bicycle?" I nodded and she pointed me to a small dock not far from a huge docked freighter from Singapore. After a few minutes a small boat shows up to ferry me across the river, dropping me off at a bike rental shack. 80 baht for a day's bicycle rental and bottle of water.
You ride past a variety of dwellings until you reach the park entrance. Sri Nakhon Khuean Khan Park and Botanical Garden is tucked inside a curved section of Chao Phraya River, in Bang Kachao (literally "pig stomach" due to it's shape). Known as the "green lung" of Bangkok since it "benefits the physical and spiritual health of the fast-growing city's residents," you truly feel like you're in the jungle as you hear mostly birds as opposed to the constant churn of Bangkok traffic. There's a nice nature trail with signage that goes around a lake. It was so humid, the inside of my camera lens fogged...but the photos would've been great.
On the way out I stopped for an excellent lunch on the side of the road, just outside the park. Communication wasn't much more than "thank you," a big smile, and a thumbs up because it was so good, but they understood.
Second, I met a group of local expats, Thais, and American friends visiting them...after dinner we grabbed a Chang from 7-11, which are never more than a couple steps away and sell everything. We made our way up to their luxury studio apartment's 27th floor rooftop, in a hip artsy part of town, with the best of views. This very nice place goes for $450/mo including gym and pool.
One in the group was from Michigan, with a "989" area code. Another was from Ann Arbor and went to MSU. And another was a Swede who recognized my Michigan accent based on how I pronounced a few words, because in grade school he had a teacher from Michigan.
The top tourist attractions can be great and worth the visit. I do some of those and enjoy them. But these experiences and places where the locals hang, that you can't plan, and not even the best tour guide could hook you up with...these are the best.