Keystone Development + Investment has signed two new leases totaling more than 60K SF at The Washington, its 880K SF office building at 510 Walnut St., and renewed one of its largest tenants. The oversized ground floor has been leased to Impact Museums and Lighthouse Immersive, the partnership that brought the immersive Van Gogh Experience to Philadelphia last year as a traveling exhibition. The nearly 32K SF space is scheduled to open early next year.