distance between tower of london and portobello market

wealdroam

An Anytime Day Single from Gatwick to Blackfriars is £10.40.
Depending on the time of day, an £8.00 Super Off Peak Single is available.

Use your Contactless payment card (or Oyster) from Blackfriars underground to Tower Hill and you will be charged £2.40 each.
A short walk from Tower Hill to your hotel.

You can continue to use your contactless card for the remainder of that day and the maximum you will be charged if you stay within zones 1 and 2 is £6.60.

Use your contactless travel on your other days and that £6.60 per day still applies as long as you stay in zones 1 or 2.

On your last day, do the reverse of your first day.

A quick google shows that a taxi each way might cost you up to £60.