Venus's surface is hot. If we dig and cover ourselves with regolith, will the temperature increase or decrease as we dig? If decrease, how far would we have to dig in order to have reasonable (say sub 100C) temperatures to put a habitat?
Due to thermodynamics, the temperature must increase.
Heat flows from hot to cold, and can not go the other direction. If there is a cold pocket between the (hot) core and the (hot) atmosphere of Venus, heat will flow into it. For it to remain cold, this heat would have to be dumped elsewhere, but since there's no colder place nearby for it to leak heat, it will heat up until it reaches an equilibrium with the core and the atmosphere.
Therefore, you can not dig down on Venus to find a layer with habitable temperatures.
While there is still much research to be done on the geology of Venus, one estimate I could find models the geothermal gradient of Venus as 25 K/km, that is, increasing as you go down.
To find 100ºC temperatures on Venus, you would instead have to go up in the atmosphere, where heat can leak into space.
The geothermal gradient on Venus may be no higher than 14K/km, that it get's warmer (not cooler) with increasing crustal depth. Locally crustal units are not closed systems but in exchange with adjacent parts, heat from below and atmosphere from above, so the gradient may be 0 or even negative, for instance when fluids take heat away or in subduction zones (on earth). The subducting crustal parts are naturally much colder than the surrounding.
But this style of tectonics does not exist on Venus, though it is assumed that plume activity creates an environment where short lived subduction around a plume that penetrated the crust can exist, that is, where crustal units at shallow depth could be colder than the overall gradient suggests.
But since the surface temperature on Venus is so high and subduction like features are situated in the planet's lower regions there is not really a chance that anywhere in the Venusian crust pockets might exist with temperatures in the suggested range of <100°C.