Osaka Gardens is located in Jackson Park, just behind the Museum of Science and Industry. Best access is to take Lake Shore Drive (either N or S) to Science Drive - which is an access street to the east and south sides of the museum and the marina. Follow the access road to the left (south) and park at the end of the lot. Walk west across the bridge and follow the path/signs to the garden.
Osaka Garden is treasure which, unfortunately, is slowly being diminished by individuals who possess a lack of regard and respect for nature/conservation. Nvtls, it is surprising that Osaka Gardens still remains relatively unknown by a lot of people that i've talked to who have lived in Chicago all of their lives - and on the south side. The best time to visit the gardens, in my opinion, is on a cool morning that's absent of mosquitos and possible rraff.