To be honest with you, I am not a big fan of big cities, but Osaka is an exception for sure. It lies about 20-40 minutes from Hirakata, depending on how deeper in the city you want to go. Kyobashi is, in my opinion, the closest stop.
Sinshaibashi is where I hang out often since there is a huge concentration of bars, pubs and clubs there. Basically, Osaka is where you want to party! My favorite pub was the English pub not far from the station. Some of the clubs I went to were Vanity, Wax and Pure. However, Pure had more people in their 20s as opposed to other so I prefer it over others. The best of it all, the club offered Nomihodai, an all you can drink fiesta!
Other than party and drinking, Osaka also has a magnificent castle called the Osaka Castle where one can behold amazing Sakura blossoms in the season. It is magnificently built and strategically placed on two levels of water to keep it from enemy attacks during the Edo period. Yes, Osaka does have some historical sites!
Apart from that, there was Kanransha, a huge Ferris wheel, at the Hep5 building which I recommend one to go with someone special. The view from the top of the city is amazing, something that I intended to and, did share with someone special.