Metal Catwalk
Metal stairs and catwalks are essential for that industrial look.
Upgrade path
Hit a placed block with a stone axe, claw hammer or nail gun while carrying the material of the next step.
Also upgraded from 
Metal Catwalk Bent, Trap (4× Forged Iron).
Harvest drops
Iron× 10
Taken apart with a harvesting tool (axe, pickaxe, shovel), before perks and tool bonuses.
When it collapses
Falling, it leaves 
Scrap Metal Pile (60% of the time) where it lands.
Where to find (81 POIs)
Crack-a-Book HQ (tier 5), Higashi Pharmaceutical (tier 5), Navezgane County Jail (tier 5), Navezgane General Hospital (tier 5), Pop-N-Pills Factory (tier 5), Red Mesa Compound (tier 5), Shamway Factory (tier 5), Shotgun Messiah Factory (tier 5), Two Bit Tower (tier 5), Camp Hollow Point (tier 4), ChemTech Distribution Center (tier 4), Don Vittorio Spagetto Residence (tier 4), Flushing Rule Palace (tier 4), Fort Quonset (tier 4), Hotel Zombona (tier 4), HSP Logistics (tier 4), Ironwood Paper Mill (tier 4), Pass-N-Gas Store #05 (tier 4), Pete's Outlet (tier 4), Richard Munchz Plaza (tier 4), Super Shamway (tier 4), The Mortician's house (tier 4), The Wright Residence (tier 4), Wasted Stiff's (tier 4), Water Works (tier 4), Carl's Cars (tier 3), Downtown Apartments (tier 3), Haulwell Freight (tier 3), Jack's Lumber Mill (tier 3), Johnnytown (tier 3), Navezgane Fire District #3 (tier 3), Pass-N-Gas Refinery (tier 3), Pop's Pawn & Bel's Bakery (tier 3), Ranger Station Alpha (tier 3), Shamway Warehouse (tier 3), Taylor Manor (tier 3), The Bear Den (tier 3), A1 Auto (tier 2), Bart's Salvage (tier 2), Boar Barn Fields (tier 2) and 41 more.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.