Mayfield Gardens are located about a 1.5 hour drive from Katoomba. It is a large privately owned garden with 75 hectares to explore. The garden only has some of it accessible for most of the year with the full garden open during the festival weeks of the year. More information about when the gardens are open can be found on their website
There is a wide variety of different gardens to explore and you could easily spend most of the day roaming around the various gardens. You can either pack a picnic or their is a cafe located on site but be aware that it is best to make a booking before the day to guarantee being able to eat at the cafe as it can be quite popular.
Some of the notable features of the gardens include extensive water features throughout, row boats, hedge maze and a flying fox.
The cost to enter the gardens is $25 for an adult with is more than reasonable considering the size of the garden. I would certainty recommend visiting the gardens if you have the opportunity.
Below are a few photos from the gardens.