This is the Ananke Nereide Flying Submarine by Lylanna Dibou and Carrah Rossini, a full-featured steampunk-themed sub which sells for L$2499 (about $9.50, at current Linden Dollar-to-US Dollar exchange rates.) It was suggested by Valentina Kendal in New World Notes' Open Forum search for SL's most precious item, as determined by its beauty, price, and other variables.
What's your nomination of SL's most precious item? Go to the Open Forum, read the criteria, and post your suggestion in Comments.
Image: from the Ananke Nereide Flying Submarine's XStreetSL e-commerce listing.