Why wouldn't Animate Tools work?

[BearonVonMu]

The party is being tasked with attacking and overcoming a castle/stronghold/guardhouse.
We have a significant period of time to do it in and have the element of surprise.
Is there a reason why the cantrip Animate Tools could not be cast many times (including its ten minute casting time) over a period of several days to undermine the whole structure and cause it to collapse into a hole?
I am already accounting for guards spotting someone casting spells nearby for hours at a time, for the dirt that would be removed, and for having multiple shovels and picks to animate.

[Drakevarg]

Mining isn't that easy. Even with the consideration that magical tools could work around the clock at a steady clip, mining a pit big enough to make an entire castle fall into a sinkhole would take months, if not years.

Now, that's not to say the effort is pointless. Undermining has been used in sieges pretty much ever since fort walls stopped being flammable. But the trick is to either dig a hole into the fort (at which point you can send a force through) or just dig underneath a wall or tower, burn down the wooden supports of your mine, and let that section collapse.

Bringing down the entire structure is a ludicrously impractical effort, but simply bringing down a wall to get in is totally doable, provided your goal is to get an army in there. If it's just the party acting as a strike team, there are faster ways.

[Zanos]

All the same problems any army of commoners with shovels would have, probably.

[ngilop]

The party is being tasked with attacking and overcoming a castle/stronghold/guardhouse.
We have a significant period of time to do it in and have the element of surprise.
Is there a reason why the cantrip Animate Tools could not be cast many times (including its ten minute casting time) over a period of several days to undermine the whole structure and cause it to collapse into a hole?
I am already accounting for guards spotting someone casting spells nearby for hours at a time, for the dirt that would be removed, and for having multiple shovels and picks to animate.

Not really.. But you are looking at a TON of time for this to happen

not to mention the fact that at some point you are going to need to shore up the mine you are digging under the castle wall or else its going to collapse ( not in the way you want) and all those tools are going to be destroyed.

[Coidzor]

The party is being tasked with attacking and overcoming a castle/stronghold/guardhouse.
We have a significant period of time to do it in and have the element of surprise.
Is there a reason why the cantrip Animate Tools could not be cast many times (including its ten minute casting time) over a period of several days to undermine the whole structure and cause it to collapse into a hole?
I am already accounting for guards spotting someone casting spells nearby for hours at a time, for the dirt that would be removed, and for having multiple shovels and picks to animate.

If you've made it so that no one can see it or hear it, or can't do anything about it even if they do, then, yeah, there you go.

Of course, if you're able to make it so that no one can physically or magically interfere with the tools, you might as well just take over the fort directly, or go through the gate, unless you really want the castle to be destroyed rather than taken.

[Psyren]

If you've made it so that no one can see it or hear it, or can't do anything about it even if they do, then, yeah, there you go.

Of course, if you're able to make it so that no one can physically or magically interfere with the tools, you might as well just take over the fort directly, or go through the gate, unless you really want the castle to be destroyed rather than taken.

There's middle ground between these - maybe the tools carve a backdoor into the fort that a small squad could use to compromise the fort's defenses (lower the drawbridge, raise the portcullis) etc. A fort that protected against, say, flight and teleportation might not have thought to protect against something simpler like that.