u3a Learn and Share activities* for u3a members cover challenges and projects and competitions. There's quite a range of projects you can engage with - some suit individuals and and some will suit a local group. You may well connect with u3a members far afield. Some activities are one-off events and others run over a period of time. See this on the national u3a website here: https://www.u3a.org.uk/learning/national-programmes
*Our local u3a benefits from the effort, support and guidance of a national u3a umbrella organisation called the Third Age Trust. The initiative above is one of their many projects.