Ailbhe,
the bridge making activity from Curious Minds (and in Irish ) uses paper to make bridges – and I have tried this with 7-8 year olds and they find it surprisingly hard to get bridges made and tested within 40 minutes. As long as you allow plenty of time (perhaps over a few weeks) this can really work. Amazing triangles / (in Irish) is a good initial activity, to help the children explore what structures are strong.