En éste caso se refiere a una área elevada, terraplén, montículo etc. Por ejemplo: donde se puede colocar un atúd, un juego de joyas, etc

Please.. I apologize.. I miss click on my computer..

It seems to be a temporary structure.

Lenin's permanent container is referred to as a glass sarcophagus in wikipedia and elsewhere.

http://www.jewishworldreview.com/0304/lenin.asp
https://en.wikipedia.org/wiki/Lenin's_Mausoleum

I think what we're talking about here is in fact an "exhibiting cold room". If you look at the photos ("Salas de Velatoria") on the website for which the URL is given below, what is shown looks like a two-room setup: one room for those viewing the remains; and the remains in a separate room, presumably refrigerated to preserve the remains, & behind glass windows ("acristalado"), with curtains even. The first meaning for "túmulo" given in the DRAE is: 1. m. Sepulcro levantado de la tierra. So the basic meaning is an elevated tomb or sepulchre; in this case, an elevated platform for the temporary display of the remains, so that family & friends can view them (from behind the glass). It seems a little weird to me - somehow, supersanitized & remote; I've gone to open-casket funerals in the US, & the casket was there on a stand; you walk up to it, you look down on the remains, say a prayer or whatever, then walk away.

http://tanatorioaller.com/servicios-e-instalaciones/

http://www.inoxcoca.com/inoxcoca/SALA CAS.html

As in the pictures in the links.

For the record.