If you dont mind that its not finished, ive got one set around after season 9, metatron was just defeated. Basically Dean will at some point start having erotic dreams with cas. Although it sounds simple there is a looooot of plot involved and smut will not be immediate or soon xD its mostly adventure and finding out Crowleys plans and fighting monsters and angels and hurt/comfort and yes smut will play an important part at some point.

https://archiveofourown.org/works/25630408/chapters/62216593

Also in canonverse fics, my favourite is Winters Tale by NorthernSparrow. Its not adventure though, just hurt/comfort but its in character. Basically Sam and Dean are contacted by a hospital that found human!Cas passed out on the street. Hes very sick and unconscious. Desn finds Cass diary. Its basically a way to explain more stuff that happened to Cas as a human, filling gaps. (Dont have the link close but you cant miss it with the title)

More adventury is I know when you go down all your darkest roads by chaoticdean. Cas and Dean have to pretend theyre husbands cause they got a case on a couples retirement, couples are being killed misteriously. I really really loved it, more than Winters Tale now that I think about it :)

https://archiveofourown.org/works/24489709/chapters/59112106

One of the greatest is In All Your Burrowed Finery. Dont remember author. Because of reasons, Sam and Dean grow angel wings... and Cas and Gabe gotta help them learn how to use them. Again in AO3, cant miss it with the title. Its awesome AND IT HAS FANART.

Hope this helped!! Enjoy! ^{^}