The Provincie Utrecht (Province of Utrecht) is named after ist capital Utrecht city.
In the east of the province lies the Utrechtse Heuvelrug (Utrecht Hill Ridge). The chain of hills is a lateral moraine formed by tongues of glacial ice after the Saline glaciation. Moraine is composed of gravel and sand, there is a lack of actual soil, the sand is not able to hold rainwater combined with a scarcity of nutrients. This is not suitable for farming, a few days without rain can cause a complete fauilure or require expensive irrigation. As a result the whole area has been planted with pine plantations. The south of the province is a river landscape. The Vechtstreek (Vecht region), on both sides of the Vecht river, is the most attractive natural area in the province. The west consists mostly of meadows. The north had depressions created by the moraines, which filled with water forming big lakes. The bogs which formed after the last ice age were destroyed by peat digging and form now again lakes.
As you can see the geological situation does not support any natural caves at all. There are important resources in the underground like natural gas, oil, and salt, but there has been not much mining. So the only underground sites found here are artificial. And as it is difficult to dig a cellar in a lowland, because it soon fills with groundwater, there are few.