I agree with DavideG,

there is a blender exporter that can
export everything model by model
and changed it to WED format.
( as strong as it needs to be! )
or the new GED, both of these are probably your
best bet.

If you want something different than these two,
there is also Deled (not as powerful, but quick),
T.ed (the terrain editor) can help make
outside worlds. 3d World Studio,