  The teaching of general relativity at the secondary school and lower
undergraduate university levels is necessarily based on approaches with a
restricted use of mathematics. An important aspect of teaching general
relativity at this level are suitable learner activities. While a substantial
number of such activities has been reported for studying the non-Euclidean
geometry of curved surfaces, there are far fewer reports of activities that let
learners actually study spacetimes and infer physical phenomena from their
geometry. In this article we report on the digital learning environment V-SeMo
that brings sector models (Zahn and Kraus 2014, arXiv:1405.0323) into an
interactive web application. V-SeMo lets learners explore relativistic
spacetimes by constructing geodesics and assessing curvature. We describe the
didactic design and the user interface of V-SeMo, discuss the extended
possibilities of virtual sector models compared to the paper models described
previously, and present an activity on light deflection near neutron stars by
way of example. We further report on an evaluation carried out with secondary
school students. Results indicate a high learning effectiveness in both the
V-SeMo-based and the paper-based versions of a teaching unit on relativistic
light deflection. The teaching materials presented in this article are
available online for teaching purposes at https://www.spacetimetravel.org .
