You can spend some pleasant time in this zoo, however do not expect to see anything spectacular. There aren't that many animal species inside and many of them look tired. The feel of the place is good though, and you can rent a bike and go through the zoo.
Also expect some difficulty to get to Dusit Zoo (and then out of the zoo back to where you are staying) because though it is in a central location near the palaces, the area is not accessible by MRT or Skytrain. The closest BTS station is Victory Monument, which is not exactly close to the zoo.
I got down at that station and had to find my way from there. I didn't want to take a tuk tuk or cab because of the risk of being charged a disproportionate fare by the driver (which frequently happens in Bangkok). I therefore had to try to guess in which direction I had to go (using my map), then taking a bus going in this direction. Same tactic for returning to the BTS, which caused me to change buses and walk on several occasions!
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