Update: A newer release is available.
NHibernate.Spatial, spatial extensions for NHibernate, allows you to connect NHibernate to a spatially enabled database and manipulate geometries in HQL or in .NET code providing you with a fully integrated GIS programming experience.
Read documentation at NH Spatial wiki site.
Please submit your bug reports or feature requests to NH issue tracker and support questions to NH Users mailing list
Installation: In you project, add references to NHibernate.dll, NHibernate.Spatial.dll,NetTopologySuite.dll, GeoAPI.dll and to provider assembly (eg.NHibernate.Spatial.PostGis.dll).