I know it is well known that you can get creatures swimming through fortifications if they are full of water.
I have a dorfwash design which includes two fortifications with a pump on top of them, an open space at the outlet, and upramps on the other end, walls around it and filled with 3/7 water you get a handy way to get rid of gunk and clean the water by pumping it.
Sometimes having dorfs sparring on the floor outside of the dorfwash they can teleport entirely through walls (as I can't figure out how they would go up one level and then clamber over the impassable pump tile instead) and get stuck in that square.
Simply ordering someone to pumpclean the water has the added bonus of washing any trapped dorfs back to the ramps so they can leave.
seems as though you reinvented the dwarven shower
With improvements due to being able to clean the water easily!
I thought the long/thin/short bolts was there in .15, possibly even .14 or before?
could you post a snapshot?
Top floor:
There are three constructed ramps side by side inside of a smoothed wall I dug out of the stone there with a pump pointing south that can draw from there. Channel or up-ramp the output tile and remove that ramp. The other side of the 3x1 ramp is the only entrance in or out, you could widen it if you want just as long as nobody can path around it to get in without going through the water, when it gets gunky you just order a pump job and then shut it off after a second or two, and as I said before, if dorfs get stuck in the bottom part somehow, you can pump them through the fortifications.
Bottom part:
The bottom is all smoothed out and then I built two fortifications under the pump.
Designate it as a pond zone and have dorfs fill it to 3/7 unless you want to dfhack it (liquids -> w > 3 -> range 3 4 1 will do it with this design if the cursor is on the left ramp) and at that point it is just a matter of ordering a pump-cleaning when you notice the water is funky. It does cause the walls to get splattered with goop at times but if they're indoors they will end up cleaned sooner or later.
Alternate layout for the standard 3x3 staircase design:
Note that the above design has vertical bars next to the ramps because I kept getting dorfs sucked through the fortifications due to the different pump layout, it isn't a problem with the single pump version, but there is no easy way to flush them back to the proper side of the fortifications with the 4x pump version, so I just stuck bars up to keep that from happening.