The Darling Range (locally called the Perth Hills) is a region approximately 30 minutes from Perth City and has many attractions that can easily fill a day of activities. How many things you want to do is up to you.
The Kalamunda Zig Zag Museum has a fascinating historical collection well worth visiting.
For a more spiritual flavour to the day there are two Buddhist monasteries to see.
In the Spring months between August - November the Wildflower displays are just delightful.
The Bickley Valley is particularly beautiful in the winter and spring (May to October) when the valleys and orchards are lush and green and the many varieties of golden wattle trees are in bloom and there are some excellent cideries, wineries and great food.