Unity map maker like UDK or Hammer?

Is there any way to create a map like in UDK or source’s hammer tool and use it with Unity?
I’ve been thinking about just trying to make maps with blender but it seems like extra effort compared to the other possible tools.

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In UDK, you can export brushes as OBJ files (File->Export->OBJ)… which you could then bring into unity. Don’t know about Hammer though.

What you are referring to is called “BSP” tools

It’s not a feature of unity3d at this time - 31/05/2011.

It has been requested: http://feedback.unity3d.com/forums/15792-unity/suggestions/248166-editor-csg-bsp-map-creation-tool

And a community member started creating a BSP add-on, but it looks like the thread it dead: http://forum.unity3d.com/threads/33446-BSP-style-geometry-creation-tool-with-lightmapping.
The last comment in that thread suggests SketchUp as an alternative.

In the end though; learning to use a 3D modelling package (Blender / SketchUp / Maya / 3DS Max) instead of relying on BSP style map-making will only help you in the long run.

You might also be interested in Unity Asset Store - The Best Assets for Game Making
There’s an evaluation version available here RealtimeCSG