Reclaiming the old riding arena

Thirty years ago we ran a riding school and had a 20 x 40m riding arena built. For family reasons I won't go in to we closed the business and let out the facilities to a local woman who was looking for premises to run a DIY livery business.  To cut a long story short she used the riding arena as a paddock, did not keep it clean and eventually topped it over with garden mulch quality chippings. It didn't take long for them to break down. Weeds loved it. With bailifs chasing her she did a midnight flit! With family issues still to the fore we were unable to take any action and for nearly twenty years the arena lay derelict. Then following my retirement in 2017 we began to reclaim it - not to use for riding but as an extension of the garden.