You could (as I just did) type in Title: "Tunnel" and that would bring up 1483 TS12 (or lower trainz-build tunnels)
The DLS is a very user unfriendly site, and no one (but me) is going to hold your hand and lead you to wade through all the jumbled up mess of absolute garbage that the DLS is, as it is chock full of Crylic nonsensical names, multiple cloned generic images that show absolutely nothing about the asset, or No Image Available", or have a image that is so low quality that it doesn't even look like anything recognizable
Then there are the wondrously helpful creators who helped us all out so greatly by naming absolutely ludicrous, nonsensical, named assets like:
Waschenlaunge
EG Walddoerferbahn Durchgangstunnel
MK-tunnelroehre_2gl-4,5 MK-tunnelportal_2gl-4,5
Then there are the mindless, endless array of the multitudes of stupid looking monstrosities "Big Block Head" portal "Snap To Grid" tunnels that need to have the the "Snap To Grid" disabled by editing the config file changing the tunnel height to -1, which eradicates the dighole completely requiring you to manually place your own 1x1 dighole by hand instead
Then there are the absolutely fabulously stunning assets by Fred24 like: "
Tunnel 3_1 voie" which is broken from the get go ... but once you edit the config file and fix it shows up like a shining gem of a tunnel (
I can show you how to fix it)
Search
https://www.auran.com/DLS/ Title:
2tracks
2 track
2_tracks
double track
Tunnel Hermosa UP
Tunnel 2track
WS Portal-Tunnel
Tunnel_Stone TRS 2012
old stone tunnel 2 track TRS 2012
Tunnel_Concrete_2Tracks_WideOpening
Tunnel_Concrete_2Tracks_SquareOpening
Tunnel_Modern_Square_2Tracks_1
Nex 2t grey Stone tunnel mouth
Nex 2t Duchy Stone tunnel mouth
Tunnel Double Track
UK Tunnel 2track stone
JMA SHINKANSEN TUNNEL A
Detailed Tunnel 1
Cuk-Tunnel-Entrance
NEX Greybrick 2 track Tunnel mouth (10m)
SF tunnel1r stone dble retaining
My suggestion is: Abandon Trainz and find another more enjoyable hobby, as Trainz has completely wasted 10 years of my life, and is a ridiculously overly complex program
As for your blob of a mountain that resembles "Stone Mountain" in Georgia ... I would eradicate the whole idea of the mountain completely, and flatten the mountain, and put in Portals that consume and emit trains automatically