I've seen Sydney Opera House and Sydney Harbour Bridge, and of the two, the Bridge is the real standout, especially at night when it is fully lit and seagulls still swarm around it, the light reflecting off them. The Opera House is a lot smaller than you expect.
I've seen whales breaching as they migrate to their breeding grounds past Wellington Point, I've watched my kids feed wild dolphins by hand, I've seen kangaroos (umpteen times), bounding across the road as I drive, I've seen koalas running like dogs across a playing field, I've seen my driveway infested by a hundred cane toads (the next door neighbour used them as golf balls), I've been up the Eiffel Tower.
When I was a kid in Larkhill, Wiltshire when you could walk to Stonehenge and around it, unhindered and unsupervised, sitting on the stones or kicking a football, with no-one else there.
I've seen AC-DC live, and met them backstage, er....I'll think of some more later.