When you explore your place do you concentrate on what you can see above ground or do you think about what lies beneath your feet? I suspect that unless the place you have chosen is in a city, then it is unlikely to feature underground railways (although a railway line may pass through in a tunnel). Canals also use tunnels to get from one side of a hill to another.
Whilst we are on the subject of water, are there any lost rivers in your place - either buried in culverts like the Fleet river in London or lost completely where it has dried up or been diverted. The shoreline may have been changed completely or islands becoming part of the mainland as land is reclaimed.
The geology of your area will often determine what use may have been of the sub-surface, from whether there was any mining or quarrying to whether there was any underground structures built.
Whilst you walk the streets look at the manhole covers - they will give you clues as to which company supplied the water, gas and electricity in the past or local manufacturers of such hardware. In my own town where I live, a number of the water stopcock covers bear the name of a local agricultural merchants.
Archaeological features may have an effect on the existing layout of your place. Does a road follow the line of the Roman road? There is a bump in the A15 north of Lincoln where the Roman road (Ermine Street) goes around the site of a redundant church suggesting that there has been a religious site there from before Ermine Street was constructed. Abandoned streets and shops have been discovered beneath Edinburgh (St Mary's Close) and in Nottingham the caves beneath the city were used for trades such as a leather tannery and homes for the poor.
Your place may not have such exotic spaces underneath, but have you thought about cellars, crypts in the church and mausoleums in the churchyards? Having recently visited the Roman Palace at New Fishbourne, I’m trying to work out if it had any influence on the layout of the modern village.
Just because you can’t see it, doesn’t mean it is not there…..