Mikan and Yuzu had never been outside (if you don't count that time they were left in that cardboard box in a meadow somewhere) because they were so young. But little kitties grow up, and having passed the one-year mark, it was maybe time to leave them outside. They did express an interest in the big blue room: they'd look outside and even mew at you if you were outside in the yard.
So a couple of weeks ago, we closed off the gap beneath the yard door with a few planks to keep them inside the garden (and to keep other cats out) and opened the door for them. They were hesitant at first, but then went into full explorer-mode within minutes.
They like it outside. But we kept checking the yard to see if they were still there. When we brought them back inside, we gave them some kitty-candy, a trick I learned from nathreee.
One of the later times, we didn't see Yuzu anywhere, until she appeared through a gap in the hedge... She had been checking out the neighbour's garden! I got a bit nervous, so we closed those gaps off with planks too -- until they found another gap. And it's not like our back yard is totally cat-proof anyway: it's only a matter of time. So we removed all the planks and let them have free roam of the yard and beyond.
Not long after that, Yuzu came back running with a white cat after her! She ran into the house, and the other cat stopped at the door -- I chased it off. It took Yuzu some time to venture out again!
The kitties are slowly expanding their horizons. Tonight they wanted to go outside again, but what with the rain, it didn't last long! They went outside, and they slowly realised: "Uh! It's everywhere!"
It's also interesting to note that Mikan and Yuzu do not explore together. They do play around for a bit in the yard, but when one of them goes off, the other either stays behind or goes off in another direction. When in explorer mode, they are hyper-alert, and when we herd them back inside, they fall asleep very soon, exhausted.
And yet I worry. They're old enough to know better than to walk under a car, but still I worry. It's perhaps a good thing we don't have kids: I think I would be one of those over-protective fathers who constantly hovers over their kid. I would do the same thing with the kitties, if I could.