Advice on getting a Russian Visa for those staying in Apartments

Visas, Invitations & Registration

Most people will need to obtain a visa when traveling to Russia

Your  visa will usually be a tourist visa. The first step to getting a Russian tourist visa is to obtain an invitation. This invitation is a document issued by a company authorized to do so by Russian Ministry of Foreign Affairs.
This invitation will state which hotel you are staying in & that you have paid in full. Even if you are not staying in a hotel & have not paid in full! There is normally a charge for this service typically €20 per invitation.
I can recommend who for most citizenships only charge €10.81.
Having obtained your Invitation normally delivered through email (though apparently some consulates want the original) you can then apply for the visa. You typically fill out an online form (& then print it out)  using your nearest consulate. Here as some links to regional consulate sites:
If you are in St. Petersburg (or Russia) for more than 7 working days  you should register your stay. If you are confused by this just ask the company that issued you the invitation.  If you do not register nothing will bad will happen. It is an administrative thing, and is more of an issue if you choose to stay for longer, which could be the case if you get sick for example.
Russian citizens need to get a visa to visit all but 40 countries on this planet, so they have no sympathy or understanding when you tell them how insane this process is!