To the wireless world, that which is solid to human beings is no more substantial than water and air. Radio signals shine through walls and cars and windows and people, barely diffracting, losing just a hair of their energy to thermal dissipation into the atmosphere or obstacles. The data and infostructures, so ephemeral to the flesh, were what was solid there.
But Echo's probes detected something; an anomaly in the Matrix. A place where signals vanished on contact, and did not emerge again. In this far corner, amidst so many abandoned or non-wireless-enabled structures, it could hide from casual notice...but an active probe revealed it's presence. The utter black hole in the Matrix caused by a faraday cage, or similar shielding. But on a building of this size, such a countermeasure would be ludicrously expensive.
"This thing is good for something," said Echo out of thin air behind and to the right of Thistle. "The building is shielded from the Matrix. I will be unable to make wireless connection until we're inside it's premises."
She didn't sound happy, or sad, or frustrated. She could have been reciting the contents of a grocery list. It took a great deal more than this to ruffle her feathers.