I'm sure not what you're looking for, but as a technicality: The property of an embassy is normally considered the sovereign territory of the country staffing the embassy, and not of the host country. So any time a new embassy opens, the host country is donating some land to the foreign country. North Korea opened an embassy in Belarus on Sept 18, 2016, so that's probably the most recent such case.
Okay, this looks like a word game. Of course, diplomacy is often all about word games.
Under the Vienna Convention on Diplomatic Relations (http://legal.un.org/ilc/texts/instruments/english/conventions/9_1_1961.pdf), Article 22, "The premises of the mission shall be inviolable. The agents of the receiving State may not enter them, except with the consent of the head of the mission. ... 3.The premises of the mission, their furnishings and other property thereon and the means of transport of the mission shall be immune from search, requisition, attachment or execution." And Article 23, "The sending State and the head of the mission shall be exempt from all national, regional or
municipal dues and taxes in respect of the premises of the mission ..."
The Vienna Convention does not use the words "soveriegn territory" or any similar phrase, either to say embassy premises are the territory of the host or the sender.
The US state department web site says, "While diplomatic spaces remain the territory of the host state, an embassy or consulate represents a sovereign state. International rules do not allow representatives of the host country to enter an embassy without permission --even to put out a fire -- and designate an attack on an embassy as an attack on the country it represents." (http://diplomacy.state.gov/discoverdiplomacy/diplomacy101/places/170537.htm)
So ... the embassy property is the territory of the host country, but they cannot enforce their laws there nor collect taxes there, and an attack on embassy property is considered an attack on the sending country.
And by the way, embassy grounds are normally patrolled by soldiers or other armed personnel of the sending country.
It sounds to me like a very fine hair to split, to say that the sending country sets and enforces the laws, has sole right to impose taxes, and maintains troops on this piece of land ... but it's not their land: the land belongs to another country that does NOT set or enforce any laws, impose any taxes, and is not allowed to send troops in.
In a brief web search I found plenty of sources saying an embassy is the territory of the host and plenty saying it's the territory of the sending nation. e.g. host: https://www.aleksandreia.com/2012/10/29/why-american-embassies-are-foreign-territory/; sender: http://www.lawndalenews.com/2012/08/embassy-sovereignty-is-sovereignty/; some of each: https://uk.answers.yahoo.com/question/index?qid=20070110055033AArqDLB.