The Above Ground widget shows the current height above a known starting altitude.
It reads and displays the device's altimeter value after optionally subtracting the starting height. The value is shown in metres or feet according to the device settings.
The widget is available in the Garmin Connect IQ store: https://apps.garmin.com/en-US/apps/08b35df6-459e-4cb6-9dc0-78828b6f3de1
Icon design by Skyclick (https://www.flaticon.com/authors/skyclick) from https://www.flaticon.com.