If the weather is nice, then:
Osaka Castle (right top of the page of the website choose English of language of your choice)
Park surrounding the castle will be nice walk.
If the weather is nice and has a clear view then,
Abeno Harukasu
Observation floor at 300 m (984 ft.), on the clear day will have an entire view of greater Osaka area plain, including Kobe area.
Tsutennkaku Shinsekai Area
Between Tenouji (where Abeno Harukasu is located) and Nanba/Dotonbori area, old town Osaka area. Nothing fancy, a lot of local restaurants, old-school middle-class area of what Osaka used to be few decares ago.
Spa World
Between Tenouji and Shinsekai area. Mega onsen complex, good for relaxing.