You could try any of the following ideas or activities below:

Make a picnic and enjoy it at a local park.

Build a den in your garden.

Visit a pick your own site and pick strawberries or other fruits and vegetables.

Draw or paint a picture of things you find outside e.g. flowers, birds, views.

Take photos of different views and landscapes. You could sketch/paint them afterwards.

Create a treasure hunt/scavenger hunt.

Read a book outside.

Make a simple bird feeder.

Create an obstacle course in the garden.

Camp out in your garden, if you have a tent.