Aburayama has the best night view of the whole city -- and if you have the chance to see it and the weather is clear, then it's well worth the trip. There is no way to get to the top except by car or motorbike though, and on weekends especially you'll find so many other cars there that parking will be tough if not impossible (no charge though). Along the way up the mountain you'll find a whole row of cars parked along the road with couples inside [actually they all say they're there for the view but I never see any of them actually looking out at the city ;-) ] as well as the most expensive "love hotel", Shiro, there too. Along the way there is also a popular mountain forest reserve, Shimin no Mori, which is 93.7 hectares big and offers some nice hiking during the daytime. There is also a commercial farm and pasture, Moo-Moo Land, with cattle and fresh milk products like ice cream. It also has a playland for kids and you can try milking a cow yourself. Closed on Wednesdays.
You can reach Aburayama by taking Route 557 starting from Tojinmachi station and head south all the way up the mountain until the end of the road. By bus: Take Nishitetsu buses of No.13 lines (ex. 13, 13-N et. al.) from Tenjin and get off at Aburayama-danchi stop (1 hour walk). From March to September, bus service is available from Fukudai Byoin Higashi-guchi stop on weekends and holidays, but infrequent -- check before you leave.