I would say moderately strenuous, mainly because of the gardens at Villa d'Estes. Hadrian's Villa is on a hilltop which you access by walking up a paved road. Our tour stopped near the top of the hill for a brief history and overview of the villa. The rest of that tour was fairly easy. The tour of Villa d'Estes is more strenuous. The villa is situated on the hillside and the gardens go down from it. You can choose how far down you go, but the only way back to the villa is up the hill, which includes a lot of steps. Once you are back at the villa, there is an elevator which will take you from the terrace level to the exit level, but climbing back from the bottom of the gardens is challenging. Our guide offered to let us wander the gardens at our leisure and meet back at the terrace later. That gave people who needed more time to navigate the hillside the opportunity to do so at their own pace.

The office is on the street to the right of the rail station Termini but I would think that a coliseum tour would meet at the coliseum. Call the number on the voucher or email them. They answer very quickly.