It can be a basement with 7 walls. It can be a tower in the back yard. It can be octagons lined up in the back of the lot. It can be a purchased lot somewhere else in the world. Allowed but remember if you have problems that can only be fixed certain ways, you could lose the mausoleum and then you would have failed. My suggestion no matter what you do is to have the place completely inaccessible so that all items within the mausoleum can remain unharmed by a random passerby, burglar or just someone in the house. If you choose to do upgraded appliances, those appliances can't be in use - they have to be in the mausoleum. Plants (not fruit) have to be behind a fence so that your Sims can't get to them and get rid of them accidentally.
It's all a part of your strategy how you set it up. Remember when you place items in the mausoleum, they can't be replaced because someone disposed of the plant or they ate the fruit. The elixir that is suddenly missing or the nectar bottle that may have been drunk. It has to be the exact 7 that you place when it counted for your requirement. Replacements not allowed and because you lost one of your mausoleum pieces, if you have already moved onto the next generation this means you've failed. End of HOF
