Last weekend here in Perth, Australia, we held our second annual Can'tCon ("So you can’t go to Cancon but you can come to Can’tcon") and our fourth mission of the day was The Armory. I brought Caledonia to the tourney and after some discussion with friends decided to make "concept list" to play in The Armury. With the new availability of Cadin Firststrike Donn, we can now have 5-man Wulver teams. And as heavy infantry are generally good to load into the objective room, they seemed like a good choice. But Wulvers (and Cadin) also have Climbing Plus. Consequently, upon getting first turn, I blew open the door of the Armory with a D-Charge and then ran the Wulver team into room. I then proceeded to climb them up the wall. Now, The Armory rules state that "it is considered to have walls of infinite height", so I started climbing them up as high as I could (wanting them to get out of range of my opponents weapons). My opponent (Wolfram_of_Sigil) was a great sport about it, allowing me to climb the link team up as high as I wanted (he dropped a Yan Huo prone and proceeded to pick off members of the team with a HRMC), but he pointed out that this might not actually be legal. He noted that when a model is climbing, their base is considered to be flat against the wall. And while the wall is considered to be infinite height and blocking for the purposes of LOS, it doesn't necessarily mean that there is actually anything for the model to move up. As such, it might not be possible for the models to climb any higher than the physical walls of the building. Ultimately it didn't actually matter as Wolfram_of_Sigil was able to thwart my plan (in the end, I had models 42" up the wall, but they were only armed with Heavy Shotguns so were unable to stop him from loading the room with more points worth of models), but it raised an interesting question. So, what are people's thoughts on this?
Yes. If you have to imagine infinite height walls for one reason, why not for any reason. But like everything terrain related, discuss before the game starts if you're at all able.
Basic requirement of the rule "Climb": The user's base must be in contact with a vertical surface. As it' impossible for the model to be in contact with a virtual surface, i'd disallow it. We had a similar discussion in the UK meta too, and it was widely refused as a legal action.
If you want to run the armory-climbing list (Lasiqs in suppression have also been floated as an appealing option in the past), ask the TO in advance whether they'll allow it. It's the only way to protect yourself, otherwise who knows how they'll rule it on the spot. It was discussed here https://forum.corvusbelli.com/threads/climbing-plus-and-infinite-height-of-buildings.35913/ and @ijw ruled that you can't climb the invisible walls, so a TO is likely to rule the same if you ask them in advance and they look it up. But since it's a terrain question, if they want they can always just say "these particular tables have invisible walls that are climbable." They wouldn't be contradicting @ijw's ruling, just adding terrain to the table which is a TO's prerogative. So if you want to do it, you might as well ask and maybe they'll let you.
And don't forget to discuss what the TO said with your opponent so you don't spring nasty surprises on them!
Hot take: Infinite height buildings with interiors are a dumb idea. It was originally based on a shortage of actual terrain for objective rooms, and the abstraction of a space that even the most terrain-poor clubs or people could create for the missions that required it. These days that's not needed. If there's a roof on that building, you should be able to play it as a normal building. And anyone who does want to play it as a silly infinite-height space should be ready for thing infinitely climbing inside of it.
Beg your pardon here, but there are more strategic and tactical issues with the Infinite Height central room. Namely, the "shadow" it generates for both sides' long range pieces that want to cover a significant part of the board, and AD troopers unable to land there (it counts as landing outside of the board because dispersion, this means AI Beacons break and other AD troops must be placed in their owner's Deployment zone borders, aside from Hellcats who can be placed anywhere in the deploymet zone of their owner). That being said, I don't think there is no internal roof on said "infinite height" central room, that leap in logic is akin to say the Empire State Building's ceiling of its street-level rooms is in the top of the spine XD