Just Last Crusade it and throw some dirt on the wall.

It’s technically still invisible. But as there is no clear rule for that I'd say it’s up to interpretation.

Oh dear I didn’t even know that. Well that makes it even more absurd.

Entirely unrelated, but I love how this makes it seem like magical items emit radiation that gets blocked by objects and gets detected by the geiger counter spell that is detect magic.

Ope great catch

Definitely. If one is trying to be prepared, See Invisibility lasts an hour but takes a lvl 2 slot while Detect Magic lasts 10 minutes and only takes a lvl 1 slot, so there's tradeoffs for sure.

One of the things I like about my firbolg twilight cleric is having the detect magic racial ability, too.