Connect an antenna to your computer's microphone input and you can hear VLF radio signals.
Just connect an antenna to your computer's microphone input, and you can receive VLF (Very Low Frequency) radio signals! A sound card (or built-in sound chip) with a recording sampling rate of at least 96 kHz is recommended.
Example of using this method to receive VLF signals from Russia and Europe:
SDR Sharp software (for Windows) to receive and record VLF (and many other) radio signals:
Similar SDR (Software Defined Radio) applications are available for Linux and Mac OS.
Lists of VLF stations:
Common sources of radio interference and recommended solutions:
About the accidental recording of VLF station GBR (16 kHz) contained on Mike Oldfield's "Tubular Bells" album: