There are many ways to introduce Sobolev spaces in the Euclidean setting. One of them is by defining a set of functions, which are absolutely continous on almost every line parallel to the coordinate axes. For such functions one can define gradient almost everywhere, and having it a space ACLp of all p-integrable functions with p-integrable gradient. It turns out that space ACLp is the Sobolev space W1,p. During my presentations I will show a way how to extend this idea to metric spaces, where lines are replaced by curves.