Drive to Loch Katrine (you can hire bikes and cycle around it). Just before the end of the road there is a car park on the left with a path going up past the woods on the right. Walk up that through the woods across the clearing and up the the short but steep "wee Ben An". It only takes a good half hour but on a clear day but the views across Loch Katrine to the mountains are absolutely amazing.
Alternatively, drive the road to Inversnaid on the east coast of Loch Lomond - great view - fantastics waterfall and nice cup of tea.
Conic Hill near Balmaha lower down the east coast of Loch Lomond is also worth the effort for the views.
Sorry, was n't into off-rading when I lived up there - I was a RAMBLER !!!!
David