The cavernous, ancient Westminster Hall, dating to 1097, where the late Queen Elizabeth II lay in state, is resolutely immune to getting any internet or mobile phone reception; highly impractical if you are arranging to meet people there who are running late and messaging you to say so.

en.wikipedia.org/wiki/Picocell

A picocell is a small cellular base station typically covering a small area, such as in-building (offices, shopping malls, train stations, stock exchanges, etc.), or more recently in-aircraft. In cellular networks, picocells are typically used to extend coverage to indoor areas where outdoor signals do not reach well, or to add network capacity in areas with very dense phone usage, such as train stations or stadiums. Picocells provide coverage and capacity in areas difficult or expensive to reach using the more traditional macrocell approach.[1]