In my current 40.10 fort, my first winter, a 10 goblin siege shows up, I set the Civilian alert, everybody should stay in the "Inside" burrow, I lock all my doors and leave only one open to bait the goblins to come where I want them....
Meanwhile my expedition leader finally gets some free time to finish the meeting with the dwarven liaison that came in autumn and is still here, they review the documents, she shows me what they want from my fort and says her farewells and beelines to the only open door to the outside that I'm using to bait the goblins...
The goblins approach the door, I lock it, and open another one further away... the liason also approaches the open door and I lock it to prevent her to go out just to encounter 10 goblins head on... I do this a few times until the goblins are too spread around my above ground walled in and roofed with retractable bridges fort area...
So the fort is in complete lock down, the only ways something might get in or out at this point are:
1) a building destroyer knocking down my above ground fort doors, which I'm prepared for: retreat to my underground fort which is safe behind a floor hatch that can only be accessed from bellow... and
2) a flyer that can fly over my unfinished underground access tunnel that needs a bridge built over 10 tiles of 7/7 water...
Well... the liaison took option number 2!! she somehow climbed/jumped/walked on water/flew/parkoured over 10 tiles of 7/7 water covering ramps like this:
the green line shows the path she took, bellow that there are ramps covered in 7/7 water, she just walked (albeit slower) over the "downward slopes", she never fell to the lower level, she's completely dry so she never touched the water...
What did she do? climbed across the sand walls?