The recently revised "Northern Ireland Primary Curriculum" recommends that teachers make use of the environment to extend children's understanding of mathematics. One approach to using the environment in mathematics is to take children on a mathematics trail. A mathematics trail uses the resources and features within the environment as a stimulus for mathematical activities. Buildings, pathways, gardens, playgrounds, forests--the environment is rich in opportunities to develop mathematical knowledge, skills, and understanding. Mathematics trails can take place indoors or outdoors and they are becoming increasingly popular at different historical sites around the country. With adequate planning and preparation, it is also possible to create a mathematics trail for use within the school grounds, or school community, and therefore tailor the activities to suit the children's needs, aptitudes, and abilities. A mathematics trail can allow children to make connections between the mathematics they are learning inside the classroom and the mathematics they experience outside. In this article, the author reports on taking mathematics "outdoors."