Some excellent material here at Leeds Beckett University (though not easy to find unless you know about it). Get hold of a theodolite, or make a clinometer, instructions included, and take some real measurements.

Virtual maths height of a tower link (includes worksheet and helpful diagrams).

Theodolite poster information from Virtual Maths

The British Museum has a KS3 challenge to find the height of a tower in its great court (February 2016). BM KS3 Maths Challenge.