Walking Challenges: Before embarking on your first Walking Challenge, you will need to download the what3words (W3W) App onto your device. This is what you will use to guide you to each clue location. For each clue, simply enter the given W3W location into W3W and follow the directions. The clue will not always be exactly at the W3W location, but will always be very close by. Virtual Challenges: Access the W3W website on your PC or laptop. After entering the W3W three-word location, you will need to enter Google Street View so that you can look around for your clue. Google Street View works in tandem with W3W, so once you get the hang of it, you will find it easy to use. If you are new to W3W / Google Street View, please click through to 'W3W / Google Street View' under Customer Service in the 18 Clues website footer (www.18clues.co.uk/w3w-google-street-view).

What3words is a geocodng system that divides the world into three metre squares and gives each one a unique three-word address. It is based in London, but is used all over the world to find, share and save precise locations.

Aside from location and backstory, the Walking and Virtual Challenges are quite different. All clues and the final solution in the Walking Challenge differ from those in the Virtual Challenge. So, many who are in a position to do the Walking Challenge, also purchase the Virtual Challenge to complete at home.

The majority of clues are based on objects that are unlikely to disappear. However, occasionally clue material may be destroyed, obscured, removed or meddled with. We are soon alerted to such changes, and make amendments to our Challenges as quickly as we possibly can. Whenever a Challenge is updated, a new edition is published. The edition of your Challenge may be found at the base of the Solution Page in the Challenge booklet (in the right hand side of the URN box). To find the most recent edition of the same Challenge, select the Challenge on the website, select the Challenge Version in the drop down menu at checkout, and you will see the current edition of that Challenge on the top right hand side of the Challenge image to the left - eg [e1]. If the edition number on your Challenge booklet is two or more less than the current edition, you may contact us here to request a PDF of the most up-to-date edition.

You can complete a Walking Challenge at any time, although we recommend that you start it early enough to reach the last clue during daylight hours. If possible, you may like to check in advance that there are no majer events taking place at the Challenge location that may impede your experience. Virtual Challenges may be undertaken at any time. You can complete them in one sitting, or in small spurts - whatever suits you best. There is no time limit to completing either Challenge, although if the current prize on offer is one that you are particularly interested in, you may like to make sure that you have submitted your answer before that prize draw expires. A new prize package comes into effect quarterly - ie every three months. For further details, see www.18clues.co.uk/prize_draw .

Needless to say, we are unable to provide you with a full set of answers to a Challenge. However, you may request the answer to a maximum of two clues if you get stuck or if a clue has disappeared (see 'I've No Clue!'). Remember that your URN may only be used once to submit an answer. If you submit the incorrect answer, you will not be entered into the prize draw.

You may use our 'I've No Clue!' facility to request the answer to up to two clues. You can do this by clicking on 'I've No Clue' at the top right of the home page of our website and clicking on the relevant Unique Reference Number (located on the Solution Page in your Challenge booklet), plus the number of the clue you want help with. This facility is completely free of charge and we encourage you to use it to increase your chances of solving the Challenge and entering the prize draw.

You know your pet best, so we will leave this to your discretion. It is vital, however, that you keep your precious pet on a lead, and safe. Remember to take plenty of 'poo' bags, and clean up after your dog as and when necessary.

Winners are notified by email within seven days of the prize draw, and their Unique Reference Number (URN) will be published on our website at the same time. For full Prize Draw Ts & Cs, please click here. Our prize draw 'quarters' run September - November, December - February, March - May and June - August. There will be a different prize package on offer in each quarter. Each new prize package commences at 00:01 on the first day of the new quarter (ie 1st September, 1st December, 1st March, and 1st June) and closes at 24:00 on the last day of the quarter (ie 30th November, 28/29th February, 31st May and 31st August). The final day of the current Prize Draw may be found on the Home page.

You can only enter the prize draw once with each Challenge booklet and accompanying URN.

Our 18 Clues Challenges are currently only open to residents of the United Kingdom. For full details, please see the Prize Draw Ts & Cs.

Yes, we offer a 20% discount on purchases of two or more different Challenge booklets in one transaction. Please note that you are unable to purchase more than one booklet of a specific Challenge in a given transaction.