I2P allows accessing the raspberrypi no matter where it's located as long as it's connected to the internet.
After first setup, on the RaspberryPi lookup and note down the i2p-address in the device (on RaspberryPi):
for f in /var/lib/i2pd/*keys; do echo "$f: $(head -c 391 $f | sha256sum | cut -f1 -d\ | xxd -r -p | base32 | tr '[:upper:]' '[:lower:]' | sed -r 's/=//g').b32.i2p"; done
On local computer start i2pd (and wait a bit):