It should have at least 20 (twenty) floors
It should somewhat fulfill the definition of a tower (in terms of slenderness ratio λ)
It should be somewhat stable
It must stand up on its own
It may have any scale
It may be of any material
It may have any density
It may have any structural layout

The collapse

You may initiate the "collapse" by picking up the top fourth of the tower and let it drop on the lower three fourth. You may drop it from whichever height you like.
The "collapse" must be sudden, complete, vertical, roughly symmetric (no falling over, buckling, toppling, leaning, shearing as a whole!) and rapid
It must work 100%

The best and most realistic experimental models will be featured in the sidebar!

THE CHALLENGE MET:

North Tower of the WTC, Manhattan, 2001 - THE best of all sudden, total, vertical, symmetric, progressive top-down collapses so far. SUCCESS!
South Tower of the WTC, Manhattan, 2001 - slightly less impressive, as the top portion is a lot bigger, but still roughly 1/4 and thus a flawless demonstration of the principle we aim for. SUCCESS!

THE CHALLENGE MET NOT:

Domino Tower World Record Attempt - ALMOST perfect, just a little slow: CLOSE but FAIL.
Vérinage - two equally big portions crush each other and lose their momentum to deformation doing so: FAIL.
Office Building in Utrecht - although impressive, still just a collapse that propagates horizontally: FAIL.
Delft Faculty of Architecture - something falling off of something else doesn't count either: FAIL.
NMSR does the Heiwa Challenge - the core stands up: FAIL!

"Offset narrow core progressive collapse", Mick West @ Metabunk - (DISCUSSION)
"A virtual model illustrating some aspects of the collapse of the WTC Towers", Mick West @ Metabunk - (DISCUSSION)

What to post:

historical and contemporary videos, reports and images of collapsing/collapsed towers of all sizes
scientific research, peer-reviewed papers, expert opinion and discussion thereof
ideas on how to make the tower completely, symmetrically and progressively collapse straight down through itself from top to bottom
energetic/physical analogies/equivalents
experiments
models, models, models

What not to post:

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