In my neighbourhood it has become popular to build "bee hotels" to have in the garden. They are commonly built by cutting logs into lengths, stacking them up and drilling multiple holes in one end of each log, each hole sized just enough for a wild bee to enter.

However, the holes need to be deep enough for the bees to be safe from bee-eating birds. Otherwise, the log will instead function as a bee trap, allowing a bird to pick off one helpless bee after the other.